66: AI Habit Tracker & Streaks

Build one life-changing habit in 66 days, guided by your personal AI coach. Backed by real habit science from University College London.

Most habits fail because the advice is wrong.

You've been told it takes 21 days. That's a myth invented in the 1960s.

Researchers at University College London studied real people forming real habits and found the true average is 66 days. Published in the European Journal of Social Psychology, the study tracked 96 participants over months and found that consistency, not intensity, is what makes a behavior automatic.

66 is built around that science. Every feature, every day, every session.

WHAT MAKES 66 DIFFERENT

Most habit trackers give you a checkbox. 66 gives you a full daily experience.

Daily AI article Each morning, 66 generates a personalized article written specifically for your habit, your goals, and exactly where you are in your 66-day journey. No generic advice. Content that speaks to what you're building.

Daily AI audio session A narrated audio session drops every day. Listen while you commute, work out, cook, or wind down. Your habit coach in your ears, every single day.

AI chat coach Ask anything. The built-in coach answers questions, helps you work through setbacks, and keeps you motivated when the streak feels hard to maintain. Available 24 hours a day, always in context.

Very few habit apps combine all three.

PICK YOUR HABIT. COMMIT TO THE JOURNEY.

Choose from 22 built-in habits across six categories:

Mindfulness - meditation, breathing, journaling Fitness - daily movement, strength training, running Nutrition - eating habits, hydration, meal planning Productivity - deep work, digital detox, learning Sleep - wind-down routines, consistent sleep times Daily habits - gratitude, reading, cold showers, and more

Or create a fully custom habit. 66 adapts to whatever you're building.

Set your personal goal. Share how you're feeling. 66 tailors every article and audio session to you.

TRACK EVERY DAY OF YOUR 66

Visual 66-day timeline showing your full journey Calendar view to check off every day you showed up Streak counter to keep the momentum going Unlockable badges to celebrate every milestone Daily reminders so you never miss your one habit

THE SCIENCE IS CLEAR

Missing one day does not break the habit. What breaks habits is inconsistency over time. 66 is designed to make showing up the easiest part of your day, so by day 66 the behavior feels automatic, not effortful.

One habit. 66 days. Build it for life.

66 PRO

66 Pro unlocks daily AI articles, narrated audio sessions, the AI chat coach, and everything else 66 has to offer.

Subscription options: Monthly: $9.99 6 months: $49.99 Yearly: $95.99

Payment is charged to your Apple ID account. Subscriptions renew automatically unless canceled at least 24 hours before the end of the current period. Manage or cancel anytime in your App Store account settings.

Download 66 free. Start your first habit today.

Habit formation research: Lally, P. et al. (2010). How are habits formed: Modelling habit formation in the real world. European Journal of Social Psychology.

Terms of Use (EULA): https://www.apple.com/legal/internet-services/itunes/dev/stdeula/