Pinpoint the difference between two calendar timestamps with millisecond accuracy. The date duration calculator tracks totals across seconds, minutes, hours, days, months, and years using true calendar math.
Set the opening date and time for your calculation.
Supply the closing date and time you want to compare against.
Date Duration Calculator - Measure Calendar Differences Accurately
Compare two local datetimes and copy elapsed seconds, minutes, hours, and days. Read calendar months and years separately, using the documented month-end convention.
Measure dated instants in the local timezone
Enter a start date, an end date, and optional clock fields down to milliseconds. The date duration calculator interprets both using the device’s local timezone. An end before the start is an error rather than an automatic overnight adjustment.
The elapsed duration is the difference between the two timestamps. January 1, 2026 at 09:00 to January 3 at 13:30 in UTC spans 52.5 hours, or 2 days 4 hours 30 minutes. Local daylight-saving transitions can change the elapsed total.
Read fixed-duration days and calendar months separately
Seconds, minutes, hours, and decimal days come from elapsed milliseconds, with 86,400 seconds per fixed day. In New York, midnight March 10 to midnight March 11, 2024 spans 23 hours. A local calendar day therefore need not equal one displayed duration day.
Calendar months use anniversaries of the original start date, clamped to the last valid day of each destination month. January 31 to February 28, 2025 is one month; in 2024, January 31 to February 29 is one month. A partial month is the elapsed fraction between adjacent clamped anniversaries. Years equal the resulting month count divided by 12.
This is the calculator’s convention. Contracts, age rules, and legal deadlines may count months differently. Keep the dates and convention beside the result when that distinction matters.
Precision and copying
Select 0–6 decimal places for numeric totals. DD:HH:MM:SS omits the fractional second and splits elapsed time into fixed 24-hour groups. Copy individual readings or Copy Summary; this page does not download a spreadsheet.
Calculation takes place in the browser. The page also uses the analytics and advertising services described in the privacy policy; local arithmetic is not a promise of zero tracking. Use Time Duration with Breaks when you need to subtract pauses.