DATE CALCULATOR
The browser handles leap years and month lengths automatically. Negative results in “between” mode mean the end date is earlier than the start. Negative numbers in “from today” mode go backward in time.
Updated May 2026 · Built by Lukáš, an architect in Prague.
Formula, assumptions, rounding & limitations
Formula
days between = (end − start) ÷ 86,400,000 msdate from today = today + N days~years = days ÷ 365.25
Assumptions
- Dates are entered as ISO calendar dates (YYYY-MM-DD) via the native date picker.
- Days are whole calendar days; time of day is not considered.
- Leap years and varying month lengths are handled by the browser’s built-in date arithmetic.
- “Today” follows your browser’s local time zone.
Rounding
- Day differences are rounded to the nearest whole day.
- Approximate years use a 365.25-day average; for exact year/month/day breakdowns use a dedicated date-of-birth calculator.
Limitations
- Business days only (Mon–Fri, excluding holidays) are not modelled. The math differs by country.
- Holidays, vacation days, and country-specific work calendars are not subtracted.
- Time-zone offsets between two dates are not relevant — only calendar date difference is computed.
Does this count weekends and holidays?
Yes — it counts all calendar days. For business days only (Mon–Fri, excluding holidays), this tool is not the right one. The math is more complex and depends on country.
Is the start day included or excluded?
Excluded. From Monday to Tuesday is 1 day. If you need “inclusive” counting (sometimes used for project days), add 1 to the result.
Why is “approximately X years” only an estimate?
Because a year is not exactly 365 days — it averages 365.25 (leap years). The “years” line uses this average. For exact age in years, months, and days, use a dedicated date-of-birth calculator.
What time zone does “today” use?
Your browser’s local time zone. If you’re traveling and your device is set to local time, “today” follows along. The calculation itself doesn’t care about time zones — only the calendar date.