Comparison

66 Days vs Protocol66

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

Head to head
About

66 Days

This app helps you build lasting habits by encouraging daily repetition over a 66-day period. Set project-specific goals and track your progress with features like memos, photos, and notifications.

Highlights
  • 66-day habit building system
  • Project-based goal setting
  • Daily progress tracking
  • Memo and photo recording
  • Dark mode support
  • Push notifications
Features
Read full description

According to a landmark study by University College London (UCL), it takes an average of 66 days for a new behavior to become an automatic, lifelong habit. You don't need extreme willpower or superhuman effort. By repeating small, consistent actions every day, your brain naturally transforms them into effortless routines. 66 Days is designed to help you organize your life goals into actionable projects, maintain daily streaks, and conquer the 66-day milestone to transform your lifestyle. [ 66 Days Key Features ] 1. Project-Based Habit Building • Set meaningful goals like 'Lose 10 kg' or 'Read 20 Books' and attach daily micro-actions (e.g., 30 push-ups, read 15 mins). • Completing just one habit action per day keeps your streak alive! 2. Break Bad Habits & Quit Tracker • Track your clean streaks for quitting smoking, junk food, procrastination, or screen time. • Log reflections when overcoming cravings and watch your milestone gauges grow. 3. Insightful Analytics & Milestones • Visualize your consistency with heatmap calendars, weekly trends, and overall statistics. • Reach 66 days to enshrine your achievement in the permanent 'Success Collection' and unlock badges. 4. Personalized Cards & iOS Widgets • Customize each habit card with custom photos, elegant color palettes, and blur themes. • Stay on top of your daily routines directly from your Home Screen with beautiful widgets. 5. Privacy & Biometric Lock • Keep your personal habit journal safe with Face ID and Touch ID biometric locking. 6. Lifetime Access & Premium • Unlock all premium features permanently with a single one-time purchase—no subscription stress. Start today. In 66 days, you will meet a completely new version of yourself! Terms of Use (EULA): https://66days.epipherse.com/terms/ Privacy Policy: https://66days.epipherse.com/privacy/

About

Protocol66

Features
Read full description

66 days. 5 habits. Miss a day, start over. Protocol 66 is the science-backed alternative to extreme fitness challenges. Based on habit formation research — not bro science — it takes exactly 66 days to build lasting habits. THE RULES ARE SIMPLE - Pick 5 daily habits - Complete all 5 every day - Miss a day, restart from zero - Rest days are earned, not given WHY 66 DAYS? Research by Phillippa Lally at University College London found it takes an average of 66 days to form automatic habits. Not 21. Not 30. Not 75. THIS ISN'T FOR EVERYONE No streaks to protect you. No lives. No second chances. If you're looking for an app that goes easy on you, this isn't it. Ready to commit? -------------------------------------------------------------------------------- Privacy Policy: https://www.pocketapps.studio/protocol66/privacy Terms of Use: https://www.apple.com/legal/internet-services/itunes/dev/stdeula/

Screenshots

66 Days4 screens
Protocol664 screens

Verdict

The call

The clearest difference is device support: 66 Days at 3 against Protocol66's 1. On price, update cadence, ads and in-app purchases there is nothing between them.

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

CostPrice · In-app purchases · Ads · Monetization

Both are free to download. 66 Days sells 5 in-app purchases, starting at $1.99 per month and Protocol66 sells 3 in-app purchases, starting at $2.99 per 7 days. Whichever you choose, the download price is not the number that matters.

UpkeepUpdate frequency

66 Days ships an update every 3 weeks, Protocol66 every 2 weeks. The most recent releases landed on October 25, 2026 and October 28, 2026 respectively.

Scorecard1 real difference · 9 level
66 Days versus Protocol66: the parameters behind the verdict, then further details
Parameter66 DaysProtocol66
PriceFreeFree
Rating4.1 (9 ratings) — better—
Positive reviews72.9% of reviews—
Number of ratings9 — better—
Update frequencyEvery 3 weeksEvery 2 weeks — better
AdsNoNo
In-app purchasesYesYes
MonetizationFreemium—
DevicesiPhone, iPad, Apple Watch — betteriPhone
Requires iOS18.018.0
Further details — not scored
Size19 MB35 MB
Age rating4+12+
DeveloperEpiphersePOCKET APPS STUDIO PTE. LTD.

In-app purchases

5 purchases

66 Days

Subscriptions3
  • Premium 1 Month$1.991 Month
  • Premium 3 Month$4.993 Months
  • Premium 1 Year$9.991 Year
One-time2
  • Project Streak Recovery$2.99
  • Premium Lifetime$22.99
3 purchases

Protocol66

Subscriptions2
  • Pro Version3 Days trial$2.997 Days
  • Pro7 Days trial$19.991 Year
One-time1
  • Lifetime Access$3.99

Questions

Is 66 Days free?
66 Days is free to download, with in-app purchases available.
Is Protocol66 free?
Protocol66 is free to download, with in-app purchases available.
Do 66 Days or Protocol66 have ads?
Neither 66 Days nor Protocol66 shows ads.
Which is updated more often, 66 Days or Protocol66?
66 Days ships an update every 3 weeks, and Protocol66 every 2 weeks. Most recently, 66 Days was updated on October 25, 2026 and Protocol66 on October 28, 2026.

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