Comparison

21 Days vs Kaizen Personal Development

Price, ratings, monetisation and update history for both apps, side by side โ€” with what reviewers say about each.

Head to head
About

21 Days

Features
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Build a new habit in 21 days, starting small enough that you'll actually do it. Big goals are easy to drop. 21 Days starts you with a tiny action, about 2 minutes a day, and gives you a reason to come back tomorrow: a streak you don't want to break and a tree that grows with every check-in. โ€ข Pick a habit and check in once a day โ€ข Watch your seedling grow into a tree as you keep going โ€ข Take a rest day when you need one, without losing your streak (2 per run) โ€ข Forgot yesterday? You can still check it in today โ€ข Medals on days 7, 14 and 21 โ€ข Clear stats: current and best streak, success rate, last 7 days โ€ข Share a card when you finish your 21 days โ€ข Morning and evening reminders at times you choose โ€ข Your data stays on your device. No account needed. โ€ข In English and Thai FREE Up to 2 habits in progress at a time (finished habits don't count). 21 DAYS PREMIUM Up to 10 habits in progress, a reminder time for each habit, and Home Screen widgets. Premium is an auto-renewing subscription, billed monthly or yearly. The price is shown in the app in your local currency before you buy. Payment is charged to your Apple ID at confirmation of purchase. The subscription renews automatically unless it is turned off at least 24 hours before the end of the current period. You can manage or cancel it in your App Store account settings. Terms of Use: https://www.apple.com/legal/internet-services/itunes/dev/stdeula/ Privacy Policy: https://teezer.cloud/legal/21days/privacy/ Start today, and let's get to day 21 together.

About

Kaizen Personal Development

Features
Read full description

Get 1% better every day. Kaizen helps you build habits that actually stick โ€” based on the Japanese Kaizen method and the Atomic Habits principle. Instead of chasing goals, Kaizen helps you build a new identity: become the person who works out, reads, or meditates every day โ€” one small step at a time, 1% per day. YOUR TOOLS โ€ข Identity-based habits: tie every habit to the person you want to become โ€ข Top-3 daily planning: focus each morning on the three tasks that truly matter โ€ข Evening review: reflect in 2 minutes on what went well โ€” and what to improve tomorrow โ€ข Zen garden: watch your progress grow with XP, streaks, and a garden that thrives with you โ€ข Focus timer: work with deep concentration in Pomodoro sessions, distraction-free WHY KAIZEN? ๆ”นๅ–„ (Kaizen) means "change for the better." No radical overhauls, no all-or-nothing โ€” just small, daily steps that add up to big results. Getting 1% better every day makes you 37x better after a year. KAIZEN PRO Try Kaizen Pro free for 7 days. After that, flexible monthly or yearly billing, cancel anytime. Start today. Your future self will thank you. Terms of Use (EULA): https://www.apple.com/legal/internet-services/itunes/dev/stdeula/

Screenshots

21 Days4 screens
Kaizen Personal Development4 screens

Verdict

The call

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.

Scored on Price ยท Rating ยท Positive reviews ยท Number of ratings ยท Update frequency ยท Ads ยท In-app purchases ยท Monetization ยท Best chart rank ยท Devices ยท Requires iOS

CostPrice ยท In-app purchases ยท Ads ยท Monetization

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.

UpkeepUpdate frequency

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

Scorecard3 real differences ยท 3 level
21 Days versus Kaizen Personal Development: the parameters behind the verdict, then further details
Parameter21 DaysKaizen Personal Development
PriceFreeFree
Update frequencyEvery 3 weeksEvery 6 days โ€” better
AdsNoNo
In-app purchasesNo โ€” betterYes
DevicesiPhone, iPadiPhone, iPad, iPod โ€” better
Requires iOS17.015.1 โ€” better
Further details โ€” not scored
Size18 MB48 MB
Age rating4+4+
DeveloperPhaisan ThauaonsamutMonica Dede Schmid

In-app purchases

None

21 Days

No in-app purchases

3 purchases

Kaizen Personal Development

Subscriptions3
  • Kaizen Pro Monthly7 Days trial$9.991 Month
  • Kaizen Pro Yearly (Offer)3 Days trial$49.991 Year
  • Kaizen Pro Yearly7 Days trial$69.991 Year

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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