A half-life anniversary marks the moment when you've known someone (or experienced something) for exactly half of your life. For example, if you're 40 years old and met your best friend when you were 20, your half-life anniversary would occur when you turn 40—because you've now known them for half your lifetime.

We use your birth date and the anniversary date you provide. The half-life moment occurs when the time since the anniversary equals the time from your birth to the anniversary. The formula is: Half-Life Date = Anniversary Date + (Anniversary Date - Birth Date).

For example, if you were born January 1, 2000 and met someone on January 1, 2010, your half-life date would be January 1, 2020—when you've known them for 10 years, which is half of your then-20-year life.

Pro users get access to 8 additional milestones beyond the half-life date:

• Golden Ratio: When time known equals 1.618× the time before meeting
• 1/3rd Life: When you've known someone for 1/3 of your life
• Quarter Life: When you've known someone for 1/4 of your life
• Double Life: When you've known someone twice as long as before you met
• Pi Day: When you've known someone for exactly 3.14 years
• Decade: When you've known someone for exactly 10 years
• 1,000 Days: When you've known someone for 1,000 days
• 10,000 Days: When you've known someone for 10,000 days

The free tier lets you track one anniversary and see your half-life date.

Pro ($1.99 one-time purchase) includes:

• Track up to 10 anniversaries
• Email and SMS reminders before milestone dates
• 8 bonus milestone types: Golden Ratio, 1/3rd Life, Quarter Life, Double Life, Pi Day, Decade, 1,000 Days, and 10,000 Days

Yes! Each anniversary has a unique shareable link that you can send to friends and family. They'll be able to see the countdown without needing to create an account.

Pro users can set up email and/or SMS reminders that will notify you before your milestone dates. You can choose to be reminded 1 day, 1 week, or 1 month before each milestone. Reminders are configured in your anniversary settings.

Yes. Your birth date and anniversary information are stored securely and are only visible to you (and anyone you share a specific anniversary link with). We do not sell or share your personal data with third parties. See our Privacy Policy for more details.

Yes. You can delete your account at any time from your Settings page. This will permanently remove all your data, including anniversaries and any associated reminders.