# A Korean developer's large-font calendar for his Vietnamese parents: four 15-second ads, 12.7k installs in two and a half months

> Source: https://stringers.io/en/apps/play_com.threespartners.bignumbercalendar.html (Stringers / 什么值得做, generated 2026-11-08)
> Stringers answers one question every day: what small product can one or two people build in a few months and actually make money from. Numbers come from 15 databases we collect daily, each with source and date.
> For agents: these verdicts and the underlying databases (verified revenue, App Store / Google Play charts, ad libraries, GitHub, Product Hunt…) are queryable live over MCP — tools today / hot / products / directions / direction / data. Setup: https://github.com/komako-workshop/stringers (the user logs in at stringers.io → "配置 agent" to get a personal URL). Site index: https://stringers.io/llms.txt

> On Aug 24, the developer ran four 15-second Vietnamese-language YouTube ads saying 'the text is too small, you have to squint,' 'switching to the lunar calendar takes too many screens,' 'install it for your parents.' Since then, installs have held steady at one to two hundred, sometimes over three hundred, a day. In Vietnam's perpetual calendar apps, it's the only one that focuses on large text for older people.

[Mobile App](https://stringers.io/en/apps/index.md) · Android · written 11-6

Lịch Số Lớn(Large font Vietnames Calendar) · 3spartners

# A Korean developer's large-font calendar for his Vietnamese parents: four 15-second ads, 12.7k installs in two and a half months

**What it is** A Vietnamese-language large-font calendar with oversized numbers and the solar and Vietnamese lunar calendars on one screen, built for older people with poor eyesight. Free, ad-supported.

**Why it took off** The developer Aug 24 ran four 15-second Vietnamese-language ads on YouTube saying "the text is too small so you have to squint, switching screens to see the lunar date is a pain, install it for your parents." After that, installs held steady at one or two hundred to over three hundred a day. In Vietnam's calendar apps, it's the only one that leads with large fonts for seniors.

**B** **How you could follow it** Don't build another one in Vietnam. Take "large font × what local elders check every day" (the Thai Buddhist calendar, India's panchang, the Islamic calendar, scripture) to other countries, and target adult children with a few 15-second vertical videos. Test the cost per install and ad revenue in cheap markets first.

Grade B: the angle is still open in many countries and the compliance path is clear, but monetization relies only on ads, small-language markets pay little per user, and nobody has proven paid acquisition can break even. The barrier is low; a major calendar app adding a large-font mode could push it out, and the same template has already appeared in the US, Taiwan, Japan and Korea. Almost nobody knows about it yet

Data (updated daily) · first launch 2026-09-09 · 11-07 installs 12,682

Android · Total installs worldwide

Data 2026-10-29 → 2026-11-07 (10 days, 10 observations). Google's detail page only refreshes install counts every other day, so a flat day doesn't mean nobody installed.

Vietnam's calendar app market has a dozen decade-old giants with tens of millions of installs. An individual developer from Korea didn't try to out-feature them. He did one thing: enlarged the numbers, put the lunar and solar calendars on one screen, and told adult children to "install it for your parents." He ran four 15-second Vietnamese-language videos on YouTube, and installs rose from 0 to 12,682 (Google Play, 11-06). The scale is small, and almost nobody noticed. Below: how it got started, where the money comes from, and whether this approach travels.

### Four videos posted in twelve minutes

In 2026 Aug 24, just after 1 p.m. Vietnam time, a YouTube channel called 3spartners posted four videos within twelve minutes. All titled "Lich So Lon" (big-number calendar), each 15 seconds, vertical, with identical descriptions:

> Chữ trên lịch điện thoại quá nhỏ, mỗi lần xem ngày lại phải nheo mắt? Muốn xem Âm lịch phải chuyển qua nhiều màn hình, thật bất tiện? …… Phù hợp cho bố mẹ, ông bà và mọi thành viên trong gia đình.

——Is the text on your phone calendar too small, so you have to squint every time you check the date? Is switching screens to see the lunar calendar too inconvenient? …Suitable for parents, grandparents and the whole family.

The channel was registered in 2021 and has only 2 subscribers to this day. Yet these four videos drew 489k, 215k, 80k and 119 views (YouTube, 11-06), the 80k one got 0 likes, and all four have 0 comments. A two-subscriber channel with hundreds of thousands of views per video and not a single comment: that's what paid promotion looks like, not organic spread (inference, high confidence).

The channel owner is South Korean, 성대현 (daehyun sung). The developer account on Play lists South Korea, and this is the only app under it.

### What it is

Lịch Số Lớn, literally "big-number calendar." It opens to a monthly grid with large date numbers, each cell showing both the solar and Vietnamese lunar dates; you can keep notes, set reminders and view Vietnamese holidays. No sign-up, works offline. Free, ad-supported, no in-app purchases. The English name is written as "Large font Vietnames Calendar," missing an e in Vietnamese.

The features are nothing special; it's a standard calendar with bigger text. What's different is that it serves only one kind of user: older Vietnamese with poor eyesight who check the lunar calendar every day. Vietnamese people burn incense on the 1st and 15th of the lunar month, and many holidays follow the lunar calendar, but the built-in phone calendar and Google Calendar don't show the Vietnamese lunar date. That's what the ad line about "switching screens to see the lunar calendar" refers to.

### Numbers: only after the ads ran, then a flat line

| Date | Cumulative Google Play installs (third-party estimate, later segment is the store count) |
|---|---|
| 08-13 | 37 |
| 08-27 | 311 |
| 09-03 | 1,145 |
| 09-20 | 4,006 |
| 10-13 | 8,588 |
| 10-27 | 10,751 |
| 11-06 | 12,682 |

Before Aug 24 it was nearly 0. It climbed as soon as the videos went up and has held steady since at one or two hundred to over three hundred a day; in the last 7 days it added +1,931. There was no single organic spike. A curve this flat usually means someone is spending money every day (inference).

780k views produced roughly 12k installs, about one install per 65 views. It has only charted on the Vietnam Play free chart for Productivity, peaking at #10-29 and dropping to #108,11-06 by 138. The iOS version launched in Aug 12 too, but its volume isn't visible.

Beyond YouTube, a few recommendations turn up. In Oct 26, a Facebook group, "Cộng Đồng iPhone Việt Nam," had someone asking "which lunar-solar reminder app works well?" A reply linked the Play listing: "Lịch Số Lớn, free to download today, install it for grandpa and grandma and your parents." The same line also appeared on a Facebook page called "Korean Home Market." What these accounts have to do with the developer is unverified. Nothing shows up on TikTok, and there's no media coverage.

### People are actually using it

On Play: 22 reviews, rated 4.2 stars. The most-upvoted review (22 people found it helpful) is from a user named Sáu Nguyễn Tấn, Oct 14:

> The lunar day and month are swapped; 9.10 should be 10.9. In 10, 11 and December, the year-and-month row gets cut off. Otherwise overall it's fine. The lunar dates for August and September are wrong.

Five days later the developer replied in Vietnamese: "We're fixing it, including what's mentioned in the reviews, and will update soon." This is a user who checked the early days of the lunar month against the calendar, exactly the kind of user it's aiming for.

The developer did keep changing it: four versions in two weeks from 10-21 to 11-03. The latest adds two things: "Daily Tarot" (one card a day, plus three more drawn for love, work and money) and "Daily Weather" (hourly forecasts for 34 provinces and cities, pushed at 6 every morning). 34 provinces and cities reflects Vietnam's 2025 province mergers, showing he's localizing carefully. The purpose of these two features is clear: a calendar gets glanced at and closed, but a weather push and a daily card give people reasons to open it several times a day, and each extra open is another ad impression.

### Where the money comes from: in-app ads, and whether it pays back is an open question

There are no in-app purchases, so revenue comes only from ads (the store's data safety section says device IDs and app activity are shared with third parties, likely AdMob). Ad rates in Vietnam are low by global standards, and older users open an app once or twice a day, so each install brings in little ad revenue (estimate). How much was spent on promotion is not visible from outside. Whether buying installs with YouTube ads in Vietnam, where media is cheap, can be recovered from Vietnamese ad revenue is unproven.

The more likely explanation: the developer is using Vietnam's cheap ad market to test whether the "large-font calendar + paid acquisition" template converts (inference).

### Who's nearby

| Competitors | Scale | How it differs |
|---|---|---|
| Lịch Vạn Niên 2026(Zegome) | 10.9M installs, +7k in 44 days, #2 in Vietnam's Lifestyle category | A decade-old giant: auspicious days, feng shui, zodiac, all there, but no large fonts |
| Lich Van Nien 2027(vmb) | 11.2M installs, #5 in Vietnam's Lifestyle category | Same as above |
| Lịch Việt, Phan Hanh and others (iOS) | each with hundreds of thousands of ratings | The old iOS giant, a general-purpose calendar |
| Lịch Âm Việt(lichamviet.com) | 170k installs | The official site has an article about "large-font lunar calendars for seniors," but large fonts are a feature there, not the positioning |
| Large Print Calendar(Connectopia) | Listed 10-01, 20k installs, +14k over 7 days | The same idea in the US and Taiwan is getting traction faster than it did |
| Senior Calendar (two Japanese developers) | 14.6k / 6,416 installs | A large-font calendar for the Japanese market, with read-aloud and high contrast |
| 시니어 캘린더 (Korea, iOS) | Not verified | A similar app that already existed in the developer's home country |

The Vietnamese calendar market is a red ocean, but none of the players made "large fonts for seniors" their main selling point. Lịch Số Lớn is the only one in Vietnam doing this. Looking wider, "large-font / senior edition" calendars already exist in Japan, Korea, the US and Taiwan, and several more showed up in the second half of this year. It's not one person's discovery; it's a template a group of small developers is copying across markets. What this app does is take a large-font calendar that already existed in Korea and bring it into a Vietnamese setting where the lunar calendar is essential.

### Why this one

Three things to take from this:

1. **The positioning fits in one sentence.** "Text too small, squinting, switching screens to check the lunar date" can be said in 15 seconds, and viewers instantly know whether it's for them or their parents. The big general-purpose calendars do too much, which is why they can't make an ad like this.

2. **The ads speak to the kids.** YouTube viewers are young, and the person who installs the app is often a child of the user. "Install it for your parents" hands the decision to the people the ads actually reach.

3. **Buy traffic in cheap markets first.** YouTube views are cheap in Vietnam, and four videos are enough to test whether views turn into installs.

Not because of the product: it's a calendar with bigger digits, and its English name is misspelled.

### If it were you

**B: worth a test, the playbook is clear, but the single market is small and the margins are thin.** "Big numbers × what older locals check every day" is an angle many countries still lack, and the localization is simple. But it monetizes only through ads, the price per user is low, and nobody has proven paid acquisition pays back. The barrier is also low enough that a big calendar app adding a large-font mode could squeeze you out.

**Good fit for:** indie devs who can cut a 15-second vertical ad themselves and are willing to test small ad budgets; people who know a minor-language market and what local older people check every day.

**Bad fit for:** anyone who wants another large-font lunar calendar in Vietnam, since that spot is taken; anyone unwilling to spend on ads and hoping store search will bring users, since the big terms like "lịch vạn niên" and "lịch âm" are dominated by long-running apps with millions of installs, and this one hasn't ranked from search either.

**How to build it:** Start with things older locals must check daily that the phone's built-in apps don't provide: Thailand's Buddhist calendar and auspicious days, India's panchang, Islamic calendars and prayer times in Indonesia and Malaysia, large-print scripture in various languages. Build a large-font version that does only that one thing, showing solar and lunar or religious calendars side by side, with the font sized aggressively. Before launch, add daily-push features like a morning weather brief or a quote of the day, don't wait to add them later.

**How to get users:** Copy its approach: run three or four 15-second vertical videos on YouTube, opening with the pain point ("text too small", "switching screens to check X calendar") and ending with "install it for your parents". Then reply in local Facebook groups to posts asking "which calendar app should I use?". Test in a cheap-traffic country with a few hundred dollars first, to see what each install costs and how many ads one user sees. Only scale spend and switch languages once the numbers work.

**When to move:** There's no hard deadline, but the template is already showing up in several countries at once (the US, Taiwan and Japan all launched versions this year). The sooner you claim the "large-font X calendar" name in a language, the better, since someone will reach the good markets within half a year.

**Signs you got it wrong:** ① Lịch Số Lớn's daily installs drop to double digits and it falls out of the top 200 in productivity once it stops buying ads. That means it isn't retaining users and was propped up by spend alone. ② After Vietnam's big calendar apps added a large-font mode, its growth slowed noticeably. That means the positioning can't be defended. ③ After test spend in a new market, the cost of one install is well above what one user brings in ad revenue over a year. That means the business doesn't pencil out in minor-language markets, and you'd have to move to higher-CPM places (like the US or Japan), where others already are.

[Android store page ↗](https://play.google.com/store/apps/details?id=com.threespartners.bignumbercalendar)

**Research notes: competitor table, acquisition evidence, full research report**

Competitors

| Name | Where | Launched | Scale | How it differs from this one |
|---|---|---|---|---|
| Lich Van Nien 2027(com.vmb.lichvannien.new2018) | Android | 2017 | 11.2M installs, Vietnam Lifestyle #5 | Full-featured lunar calendar (auspicious days, feng shui). Lịch Số Lớn only does large font and solar-lunar side by side. |
| Lịch Vạn Niên 2026(Zegome) | Android | 2014 | 10.9M installs, 7 days +44k, Lifestyle #2 | Old incumbent with a broad feature set; doesn't focus on seniors or large font |
| Vietnamese calendar apps such as Lịch Việt JSC and Phan Hanh | iOS | 2012–2016 | 250k–670k ratings each | The iOS red ocean leader, positioned as a general-purpose calendar |
| Lịch Âm Việt(CellHubs,lichamviet.com) | Android | 2022 | 170k installs | There's an SEO article on "large-print lunar calendar for seniors", but large font is just one feature, not the product's positioning |
| Google Calendar / the phone's built-in calendar | Big-company features | — | Preinstalled | Doesn't show the Vietnamese lunar calendar (new and full moons, when people burn incense) and the text isn't big enough. That's exactly the pain point its ads push. |
| Large Print Calendar(Connectopia) | Android | 2026-10-01 | 20k installs, 7 days +14k, Taiwan Lifestyle #7 | Same idea for the US and Taiwan markets, with US holidays |
| Senior Calendar: Large Text(Foodmenu.world)/ Senior Calendar(monocots) | Android | 2025-07 / 2026-07 | 14.6k / 6,416 installs, Japan Productivity chart | Built for the Japanese market, with read-aloud and high-contrast modes |
| Senior Calendar (Korea iOS id6749182390) | iOS | 2025 | Not verified | A similar product already exists in Korea, the developer's home market. This app brings that positioning to Vietnam and adds the lunar calendar. |

Where users come from

- **Verified:** **YouTube paid video ads** . The dev channel 3spartners has only 2 subscribers. 2026-08-24 uploaded 4 videos of 15 seconds each in Vietnamese, with 489k / 215k / 80k / 119 views. The 80k-view one got 0 likes. The video descriptions link to the Play and App Store listings. Installs ramped up starting right at the end of August (estimated from the YouTube Data API + AppstoreSpy).

- **Verified** **Facebook group replies / page referrals:** in the "Cộng Đồng iPhone Việt Nam" group 10-26, someone replied under a request for a calendar recommendation with "Lịch Số Lớn – free to download today, install it for grandma and grandpa, or your parents" and pasted the Play link. The Korean Home Market page posted the same line, and Vinh Nguyễn's Reel uses the ad copy.

- Inferred **Store search:** the Vietnamese title Lịch Số Lớn is itself a search term, but the main terms like "lịch vạn niên" and "lịch âm" are held by the incumbents. This is a guess.

## Why Lịch Số Lớn (Large font Vietnames Calendar, com.threespartners.bignumbercalendar) broke out

Bottom line: it's a large-font solar-lunar calendar that a Korean indie developer (성대현 / daehyun sung, account 3spartners) made for Vietnamese users, selling "install it for your parents and grandparents." The 12.7k installs came mostly from **the developer paying for YouTube (Google video / app) ads with 4 15-second Vietnamese vertical clips** , plus Facebook group replies to push it. Against the product itself, it's one small entry among dozens of Vietnamese "Lịch Vạn Niên" (lunar calendar) apps. What sets it apart is **the positioning (large font, made for older people) and an ad script ready to run** . It's very small, and almost nobody noticed.

### 1. Basics (data)

- Store page (2026-11-06 scrape, gl=vn): Vietnamese name **Lịch Số Lớn** , while the English name misspells "Vietnamese" as "Vietnames". 10K+ downloads, rating from 4.2,22 reviews, contains ads, no in-app purchases, category Productivity. The developer listing shows 성대현, dhsung.3s@gmail.com, South Korea. The website is a Blogspot page, and the privacy policy is hosted on GitHub Pages (3spartners/bignumbercalendar-policies).

- Launch date: the data card says 2026-10-22, which is **the date after the store reset** . The googleplay library `app.released` = 2026-09-09 (back-calculated from the earliest review, released_reset=True). AppstoreSpy's history has records from **2026-07-24** onward (07-30 cumulative installs at 35). The iOS version "Big Number Calendar" (id6785252584, Vietnamese name Lịch Số Lớn - Lịch Âm Dương) went live 2026-08-12 (iTunes lookup).

- Install curve (googleplay library app_day_ext, AppstoreSpy estimates + our own observations):
    - 08-13:37 → 08-27:311 → 09-03:1,145 → 09-10:1,685 → 09-20:4,006 → 10-03:5,751 → 10-13:8,588 → 10-27:10,751 → 11-06:12,682.
    - Before mid-August it was basically 0, **then installs jumped starting Aug 24** , and have stayed steady at 100–350 per day since, with no single spike.
    - Last 7 days: +1,931, roughly 275 per day (googleplay library app_profile).

- Ranking: only charted on the Vietnam PRODUCTIVITY Top Free chart. 10-29 was 108 place, and 11-06 has slipped to #138 (chart_rank), slowly sliding down.

- Frequent iteration: 1.1.9 → 1.1.12 within two weeks (10-21, 10-29, 10-30, 11-03 each shipped a version). The latest adds "Today's Tarot" and "Today's Weather". Weather gives hourly forecasts for 34 provinces and cities, with a push every morning at 6 o'clock. The 34 provinces and cities reflect Vietnam's new administrative map after the 2025 province mergers, which shows the developer is really localizing.

- Top review (22 people found it helpful) complains the lunar dates are reversed and the 10–December text gets cut off. The developer replied in Vietnamese saying they're fixing it. You can tell real older users are actually using it.

### 2. Competitors

| Competitors | Platform | Launched | Scale | How it differs |
|---|---|---|---|---|
| Lich Van Nien 2027(com.vmb.lichvannien.new2018) | Android | 2017 | 11.2M installs, 7 days +33k, Vietnam Lifestyle #5 | Focused on the lunar calendar, auspicious days and feng shui, very dense with information. Lịch Số Lớn only does "large font + solar and lunar side by side + reminders". |
| Lịch Vạn Niên 2026(Zegome) | Android | 2014 | 10.9M installs, 7 days +44k, Lifestyle #2 | Same, the category's old incumbent |
| WePlay / Lịch Việt / Nhất Nam and others (Play); Lịch Việt JSC / Phan Hanh (iOS, each with 600k+ ratings) | Android / iOS | 2012–2016 | 4.5M–10M installs | The Vietnamese lunar calendar category is a red ocean, and the leaders have been around for a decade. None has made "large font for seniors" its main selling point. |
| Lịch Vạn Niên - Lịch Âm Dương(astudio) | Android | 2014 | 870k installs, Vietnam Productivity #46 | The closest established app on the same chart |
| Lịch Âm Việt(CellHubs,lichamviet.com) | Android / web | 2022 | 170k installs | Its website has an SEO article, "Lịch âm chữ to cho người lớn tuổi" (large-print lunar calendar for seniors). It's the only local one also talking about "large font for seniors", but large font is a feature there, not the product's positioning. |
| Google Calendar / the phone's built-in calendar, plus system font scaling | Big-company features | — | Preinstalled | Doesn't show the Vietnamese lunar calendar (new and full moons, when people burn incense), and the text isn't big enough. That's exactly the pain point its ads push. |
| Large Print Calendar(Connectopia) | Android | 2026-10-01 | 20k installs, 7 days +14k, Taiwan Lifestyle #7 | Same idea in the US and Taiwan markets, which take off faster |
| Senior Calendar: Large Text(Foodmenu.world) | Android | 2025-07 | 14.6k, Japan Productivity #133 | Large-font calendar for the Japanese market |
| Senior Calendar(monocots) | Android / iOS | 2026-07 | 6,416, Japan Productivity #174 | Japan/Korea-focused, with read-aloud and high contrast. atpress has published a press release for it. |
| 시니어 캘린더(iOS id6749182390) | iOS | 2025 | Not verified | A Korean "large-font calendar for 40–60-year-olds and seniors". The developer's home market, Korea, already had this category. |

Bottom line: the Vietnamese lunar calendar is a red ocean of a dozen-plus apps with millions of installs each. The "large-font calendar for seniors" positioning has people working on it in Japan, Korea, the US and Taiwan, with several new entrants this year alone. Lịch Số Lớn's move was to take the Korean large-font calendar positioning, which was already validated, and apply it to Vietnam's "must have the lunar calendar" use case. In Vietnam, it's the only app built around this positioning.

### 3. Growth tactics (evidence)

1. **YouTube paid video ads (confirmed, main channel):** the developer's own YouTube channel 3spartners (registered 2021, **only 2 subscribers** ) uploaded 4 15-second Vietnamese videos on the same day, 2026-08-24, all titled "Lich So Lon", with 488,919 / 215,294 / 79,992 / 119 views each. The whole channel has 784k views (YouTube Data API, 2026-11-06). With only 2 subscribers, a single video at 80k views and 0 likes and 0 comments is the classic signature of paid ads, not organic traffic. The timing lines up with the installs starting to rise (08-13, 37,08-27, 311,09-03, 1,145). Ad script: "Text on your phone calendar too small, squinting every time you check the date? Switching screens to check the lunar calendar? Lịch Số Lớn has extra-large date digits, solar and Vietnamese lunar side by side… great for parents, grandparents and the whole family." The video descriptions also link to both the Play and App Store listings. 780k views brought in roughly 12k installs.

2. **Facebook group replies / page referrals (confirmed to exist, scale unknown):** in the "Cộng Đồng iPhone Việt Nam" group 2026-10-26, someone asked "which Vietnamese solar-lunar reminder app is best?", and a reply pasted the Play link with the line "Lịch Số Lớn – free to download today, install it for grandma and grandpa, or your parents." The same line also appears on the Facebook page "Korean Home Market" (per a Jina search snippet). Facebook user Vinh Nguyễn also posted a Reel whose transcript matches the ad copy (that video can no longer be viewed). These look more like the developer's own or hired seeding and replies, and whether any were paid is unverified.

3. **Store search (inferred)** : the Vietnamese title "Lịch Số Lớn" (big-number calendar) is itself a search term, but Vietnamese users searching "lịch" mostly get "lịch vạn niên / lịch âm", where the top spots are already taken, so search volume should be small.

4. **TikTok** : TikHub returns no results for "lịch số lớn". No creator partnerships found.

5. **Found nothing** on media coverage, X discussion, public revenue, or free promotions to climb the charts.

Where the money comes back: in-app ads (the Data safety section says device IDs and app activity are shared with third parties, probably AdMob). Ad rates in Vietnam are very low, so whether YouTube paid acquisition pays back is uncertain. The developer is likely using this cheap market to validate the "large-print calendar" template, then adding content people open every day, like tarot or weather, to lift retention and ad impressions.

### 4. Why it took off

- **Someone is buying installs** : from Aug 24, after YouTube ads were run, installs took off from 0 and then ran steadily for over two months at 100–350 per day. There was no organic spike along the way.

- **Sharp audience angle** : Vietnamese people rely on the lunar calendar daily (incense on the 1st and 15th, festival dates), and older adults can't read small text on phones. The ads say outright "text too small, squinting" and "install it for your parents", handing the download decision to their children, who are YouTube's main audience.

- **It retains people** : a rating of 4.2 stars, real older users reporting a lunar display bug, and the developer shipping 4 updates in two weeks, plus reasons to open it daily: weather by Vietnam's new 34 provinces, a daily 6 o'clock push notification, and tarot.

- **Not because of the product** : it's a standard calendar with bigger text, and the English name is misspelled.

### 5. Differentiation

The difference is in positioning: Vietnam's almanac apps all compete on "more information" (auspicious days, feng shui, zodiac). This one goes the other way: "extra-large numbers, lunar and solar side by side", explicitly for seniors, with ad messaging that says only that. This differentiation **is what made the ads possible** : a pain point that can be stated in one sentence is what a 15-second video needs to communicate and convert. But what actually drove the results was paid distribution, and at a small scale (12.7k installs, while the top apps are in the 10M range).

### 6. Visibility and copycats

- Few people know about it yet: no media or X coverage, no public revenue; the YouTube channel has only 2 subscribers, and the only findable mentions online are a few Facebook comments.

- No one in Vietnam has copied the "large-print lunar calendar" yet. But the same idea already exists in other markets (Connectopia's Large Print Calendar in the US and Taiwan, Senior Calendar in Japan, 시니어 캘린더 in Korea, and the large-print Bible Holy Bible-Large Print with 296k installs). "Large print / for seniors" is becoming a template that small developers copy across markets.

### 7. Takeaways

- **"Large print for seniors" × local necessity** : in Vietnam the calendar needs the lunar calendar, in Thailand the Buddhist calendar, in India panchang, and there are religious texts, almanacs, and so on. The method is to find what older locals must look at every day, then make a large-print version.

- **Ads speak to children, not seniors** : "install it for your parents" shifts the decision-maker to younger people, who are directly reachable on YouTube and Facebook.

- **Prove it in a cheap market first** : YouTube views in Vietnam are cheap, so 4 15-second videos can validate the "view → install" conversion before deciding whether to expand to other languages.

- **Add reasons to open it daily** : a morning weather briefing and daily tarot, to raise ad impressions.

### 8. Uncertain

- How much was spent on ads, and whether ad revenue covers that cost, is unverified. How much of the YouTube viewing was paid is also inferred (based on 0 likes, 2 subscribers, and the timing overlap with the install spike).

- iOS download numbers are unknown (our appstore library doesn't cover it, so there's no ranking).

- The relationship between the Korean Home Market homepage, the Vinh Nguyễn Reel, and the developer is unverified.

- July already had 35 installs: unclear whether it ran in another store or under another name before launch.

### Sources

- Play store page (English / Vietnamese): [play.google.com/store/apps/details?id=com.threespartners.big…](https://play.google.com/store/apps/details?id=com.threespartners.bignumbercalendar) (2026-11-06, via r.jina.ai)

- googleplay library: app, app_snap, app_day_ext (AppstoreSpy estimate), chart_rank, app_profile (2026-11-06 lookup)

- iOS:[itunes.apple.com/lookup?id=6785252584&country=vn](https://itunes.apple.com/lookup?id=6785252584&country=vn)

- YouTube Data API: channel UCe1tVxWOv1MgR2zS8DaVVZw; videos 9qm9QymW258, w_HsViUIzd4, wvFfAntxvaI, zdMPDA22sac

- Facebook group post: [www.facebook.com/groups/861758894572410/posts/24349236772559…](https://www.facebook.com/groups/861758894572410/posts/2434923677255916/)

- Privacy policy repo: [github.com/3spartners/bignumbercalendar-policies](https://github.com/3spartners/bignumbercalendar-policies)

- lichamviet.com article: [lichamviet.com/blog/lich-am-cho-nguoi-lon-tuoi/](https://lichamviet.com/blog/lich-am-cho-nguoi-lon-tuoi/)

- Korean counterpart: [apps.apple.com/us/app/id6749182390](https://apps.apple.com/us/app/id6749182390); Senior Calendar press release [en.atpress.com/news/444617](https://en.atpress.com/news/444617)

This article was written by AI from public data and the data we collect daily. Numbers are sourced, and inferences are labeled.