Time tools
8 free time tools · Dates, durations and zones
Date arithmetic is deceptively hard — daylight saving, leap years, month lengths and the question of whether the first day counts all conspire against mental maths. These work in whole calendar dates rather than hours, which is what stops the answers drifting by a day twice a year.
All time tools
- Days between dates Count days and optional business days between two dates.
- Age calculator Exact age in years, months and days, plus next birthday.
- Add days to date Add or subtract days, weeks, months or years.
- Time zone converter Compare a time across multiple zones at once.
- Date countdown Live countdown to any date and time.
- Duration calculator Time between two dates and times, every way.
- Week number ISO and US week numbers for any date.
- Timesheet calculator Add up worked hours with breaks and overnight shifts.
Guides
- Business days vs calendar days: why "within 10 days" is ambiguous Ten business days can span more than two calendar weeks. How business-day counting works, where weekends differ worldwide, and the counting traps in contracts.
- What "one month later" actually means (dates are harder than they look) What is 31 January plus one month? There is no single right answer — how month arithmetic works, why software clamps dates, and where the edge cases bite.
- Week numbers explained: why your week 1 is not my week 1 Europe plans by week numbers, but ISO 8601 and US conventions disagree about week 1 — and some years have 53 weeks. How the numbering systems actually work.
- Why time zone conversion is harder than adding hours UTC offsets change with the calendar, half-hour zones exist, and DST switches on different dates worldwide. Why fixed-offset arithmetic is only usually right.