# 21 Days vs Kaizen Personal Development

The clearest difference is in-app purchases: 21 Days at none against Kaizen Personal Development's 3. Kaizen Personal Development's advantage is update cadence (every 6 days vs every 3 weeks) and iOS requirement (15.1 vs 17.0). On price, ads and device support there is nothing between them.

Both are free to download. Kaizen Personal Development sells 3 in-app purchases, starting at $9.99 per month. 21 Days asks for nothing beyond the download.

21 Days ships an update every 3 weeks, Kaizen Personal Development every 6 days. Both last shipped on October 24, 2026.

## The numbers

| Metric | 21 Days | Kaizen Personal Development |
| --- | --- | --- |
| Price | Free | Free |
| In-app purchases | **No** | Yes |
| Ads | No | No |
| Update frequency | Every 3 weeks | **Every 6 days** |
| Size | 18 MB | 48 MB |
| Requires iOS | 17.0 | **15.1** |
| Devices | iPhone, iPad | **iPhone, iPad, iPod** |
| Age rating | 4+ | 4+ |
| Developer | [Phaisan Thauaonsamut](https://appshunter.io/developer/6773761501) | [Monica Dede Schmid](https://appshunter.io/developer/1873571941) |

## What reviewers say

### 21 Days

[App page](https://appshunter.io/ios/app/21-days-habit-builder/id6773761499)

**Features:** macOS Compatibility, Vision Pro support

**In-app purchases:** none


### Kaizen Personal Development

[App page](https://appshunter.io/ios/app/kaizen-personal-development/id6790007423)

**Features:** macOS Compatibility, Vision Pro support

**In-app purchases (3)**

| Purchase | Price | Billing |
| --- | --- | --- |
| Kaizen Pro Monthly | $9.99 | per month |
| Kaizen Pro Yearly (Offer) | $49.99 | per year |
| Kaizen Pro Yearly | $69.99 | per year |


## Frequently asked questions

### Is 21 Days free?

21 Days is free to download, with no in-app purchases.

### Is Kaizen Personal Development free?

Kaizen Personal Development is free to download, with in-app purchases available.

### Do 21 Days or Kaizen Personal Development have ads?

Neither 21 Days nor Kaizen Personal Development shows ads.

### Which is updated more often, 21 Days or Kaizen Personal Development?

21 Days ships an update every 3 weeks, and Kaizen Personal Development every 6 days. Most recently, 21 Days was updated on October 24, 2026 and Kaizen Personal Development on October 24, 2026.

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*Compared by [AppsHunter](https://appshunter.io/) from daily US App Store data. Review summaries are generated from verbatim App Store reviews.*