Very clever.
Fun and educational.
Free
About
This app reveals the precise location of any date within the first five billion digits of pi. Search for significant dates like birthdays or anniversaries and explore their placement in pi's infinite sequence. It supports various date formats and allows you to save and share your discoveries.
✓Find today's date in pi
✓Search for any date in pi
✓See exact position of dates
✓Compare multiple date formats
✓Explore calendar heat map
✓Save favorite dates
✓Share discoveries as cards
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What's New in Piday
1.3 (kim)
April 29, 2026
What’s New (1.3 - kim) Non-pi dates use a DDMM or MMDD format to ensure dates are found in these. Celebrations got an upgrade: featured-day popups + confetti now work for Tau Day (6/28), Euler’s Number Day (2/7), Golden Ratio Day (1/6), and World Quantum Day (4/14). Plus a handful of small fixes and polish.
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FAQ
What is Piday?
Piday is a calendar application that shows you where any given date appears within the first five billion decimal digits of pi. It helps you explore the mathematical sequence of pi in a unique and engaging way.
How does Piday work?
You can search for specific dates, such as birthdays or anniversaries, and Piday will display their exact position within the digits of pi. It also highlights today's date in pi automatically upon opening the app.
Can I search for any date in Piday?
Yes, Piday allows you to search for any date you care about. It searches multiple date formats to find the best match and shows you where it lives in the infinite digits of pi.
Does Piday have ads?
No, Piday does not have ads. The app is designed to be a clean and uninterrupted experience for users interested in exploring pi.
What devices does Piday support?
Piday is available on iPhone, iPad, and Mac. It is designed to work seamlessly across these Apple devices.
Is Piday free to use?
Yes, Piday is completely free to download and use. There are no in-app purchases or subscriptions required.
How often is Piday updated?
The latest version of Piday is 1.3 (kim), which was last updated on April 29, 2026. Updates typically include improvements and new features.
What is the age rating for Piday?
Piday has an age rating of 4+, making it suitable for a wide range of users interested in educational and mathematical content.