Pi birthday finder
Find where a birthday (YYYYMMDD, YYMMDD or MMDD) first occurs in the true first 10000 decimals of pi — 08/08 lands at position 4544 — with every occurrence and hints when an 8-digit date is absent.
Runs in your browserEvery computation happens in your browser — your data never leaves this device.
Birthday position
Positions count from the first decimal digit.
Enter a birthday to look it up
Found: 0 · First position: 0 · Occurrences: 0
What this tool does
- Turn a birthday into a fun fact by quoting its position in pi.
- Find a low position for an anniversary or launch date as an easter egg.
- Show the 10ⁿ expectation rule by comparing 4-digit dates with 8-digit ones.
Example
Input
1225
Output
「1225」（12 月 25 日（月日））在圆周率小数点后第 9416 位首次出现。 在前 10000 位中只出现 1 次。 上下文（从第 9410 位起）：79396122571429 参考概率：4 位数字串的期望出现间距约 10000 位，所以在 9416 位就出现算比较靠前。
08/08 first appears at position 4544; a full 8-digit date such as 19900101 almost never shows up in the first 10000 digits, which is expected.
Frequently asked questions
Why is my 8-digit birthday missing?
Only the first 10000 digits are searched, while an 8-digit string first appears at an expected position of about 100 million. The chance of an 8-digit date landing in 10000 digits is roughly one in ten thousand, so a miss is normal — try 6 digits (drop the century) or the 4-digit month/day.
Where does position counting start?
From the first decimal digit: position 1 is the 1 of 3.14159…, and the integer 3 is not counted, matching the usual phrasing.
Which date formats work?
YYYYMMDD (8), YYMMDD (6) and MMDD (4). Separators and Chinese characters are stripped, so 2026-01-01 and 2026年1月1日 both become 20260101.
Can the same birthday occur more than once?
Yes, especially short strings: 0101 appears twice (positions 2562 and 9985) and 9999 three times. Every position is listed, capped by the “maximum positions” field.
Is the data real?
Yes. The 10000 digits are embedded in the page, computed with the Chudnovsky series and cross-checked with an independent Gauss–Legendre run. Double-precision floats only hold 15–16 significant digits, so they cannot reach these positions.
Keywords：圆周率生日pi birthday生日在圆周率第几位π 生日查询数字位置生日检索pi day圆周率查询