Date & Time Toolkit for Data
Every date problem data people hit, in one place: Unix epoch timestamps, Excel serial dates, ISO formats, date arithmetic, and relative time — with automatic unit detection and daylight-saving-aware conversions, all in your browser.
All conversions run locally — safe for production timestamps.
Tool interface
Current time (live)
Introduction
Timestamps hide everywhere in data work — in logs, APIs, databases, JWT claims, and spreadsheets — each using a different representation. This toolkit converts between all of them and does the date arithmetic that usually requires a script, entirely in your browser.
How it works
- Unix Epoch: auto-detects seconds/ms/µs/ns by magnitude and converts to ISO, UTC, local, and relative time.
- Excel Serial: handles both the 1900 and 1904 date systems, including the phantom 1900-02-29 leap-year bug.
- Date Toolkit: computes differences, adds/subtracts intervals, breaks dates into parts, and shows relative time.
- All conversions use the browser's
IntlAPI, so daylight saving is applied correctly for the date you enter.
How to use
- Pick a tab: Unix Epoch, Excel Serial, or Date Toolkit.
- Choose a mode and enter your value.
- Click Convert / Run and copy the result.
Use cases
- Decoding timestamps in server logs and crash dumps.
- Reading
iat/expclaims in JWT tokens. - Fixing Excel serial dates exported to CSV or SQL.
- Computing intervals for reports and SLAs.
Common mistakes
- Passing milliseconds where seconds are expected (dates jump to year 50,000+).
- Assuming the epoch is local time — it is always UTC.
- Using the 1900 system on a file saved with the 1904 system (off by 1,462 days).
Limitations
- JavaScript dates are valid roughly ±275,000 years from the epoch.
- Excel date parsing here covers serial numbers, not formatted date strings.
FAQ
Is my data uploaded anywhere?
No. Every conversion happens locally in your browser.
Why did my timestamp convert to year 57,732?
The value was treated as milliseconds. Use auto-detect or select seconds explicitly.