Developer Tool
Unix time isn't the only epoch in use. Pick a date to see it in every system below at once — or paste a raw value from one of them to decode it.
Reverse
Paste a number from one of the systems above and see the corresponding date.
Excel and Google Sheets store dates as a plain number of days since December 30, 1899 — except Excel famously (and incorrectly) treats 1900 as a leap year, a decades-old bug kept for backward compatibility. The 1899-12-30 epoch already accounts for this quirk, so the numbers you see match what Excel actually displays for modern dates.
.NET ticks count 100-nanosecond intervals since January 1st, year 1 — a huge number, since it's been over 2,000 years. Mac HFS+ (the classic Mac OS filesystem) counts seconds since 1904, chosen so 1904 could be a definite leap year without ambiguity. GPS time counts seconds since January 6, 1980, and deliberately ignores leap seconds — so it drifts further ahead of UTC every time one is added (currently 18 seconds ahead, a gap that could change if a new leap second is announced). The Julian Day Number is a continuous day count used in astronomy, dating back to 4713 BC, useful because it never has the ambiguity of calendar reforms or timezones.
Working with epoch time in your actual codebase? See the Epoch Time in Programming Languages guide.
Related
The everyday Unix timestamp converter.
How to get and convert epoch time in code.
Why some of these systems have their own overflow dates too.