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Welcome to PIrthday.com!

This little app will help you to calculate the most important days in your life, your PIrthdays (or PI-birthdays)!
Just enter the date of birth for which you want to know the dates and hit the button! Have a πe (or π-pie) and celebrate with all your friends.
Further essential services on this site:
  • On Happy PIrthday you can see who celebrates his PIrthday today!
  • On Baby PIrthday you can see when you should have business time
    so the chances that your child will be born on π-day are maximized.
  • On the PIrthday Blog you can learn more about PI, PIrthdays, and mathematical celebrations!

What is a PIrthday?

A PIrthday (PI-birthday) is a special milestone that occurs every π years after your birth. Unlike regular birthdays that happen annually, PIrthdays happen approximately every 3 years, 1 month, and 23 days—making them rare and mathematically significant celebrations!

The Math: One PI-year = π × 365.25 days ≈ 1,147.35 days ≈ 3.14159 years. We calculate using minutes for extra precision: π × 525,600 minutes = 1,652,580 minutes per PI-year.

Why Celebrate PIrthdays?

  • They're Rare: You only get about 25-30 PIrthdays in a typical lifetime
  • Mathematical Beauty: Connect your life milestones to one of math's most famous constants
  • Unique Celebration: Stand out from regular birthday celebrations
  • Educational Fun: A great way to make math interesting for kids and adults alike

PIrthday Milestones Chart

PIrthdayApproximate AgeLife Stage
3 years, 52 daysToddler
9 years, 155 daysChildhood
15 years, 260 daysTeenager
21 years, 364 daysYoung Adult
10π31 years, 155 daysAdulthood
15π47 years, 97 daysMiddle Age
20π62 years, 310 daysSenior

Frequently Asked Questions

Q: How accurate is the PIrthday calculation?
A: Very accurate! We calculate down to the minute, accounting for leap years and using the astronomical year length of 365.25 days.

Q: Do I need to know my exact birth time?
A: For the most accurate PIrthday, yes. Without it, we assume midnight (00:00) on your birth date.

Q: Is this related to PI Day (March 14)?
A: They're both celebrations of π! PI Day celebrates the number itself, while PIrthdays apply π to your personal timeline.