How are months and years counted?

Whole months use clamped calendar anniversaries. January 31 to February 28 is one month in a common year; January 31 to March 1 is one month and one day. A February 29 anniversary clamps to February 28 in a common year. Twelve whole months make one year. Whole calendar months combines the year and month parts; no average month length is used.

Why can one calendar day contain 23 or 25 elapsed hours?

Local UTC offsets can change between the endpoints. Midnight to midnight across a spring-forward change can be one calendar day but 23 elapsed hours, and across fall-back it can be 25. Days and weeks count whole clock-face calendar units. Total hours, minutes and seconds are whole elapsed units, rounded down; 90 elapsed minutes shows 1 total hour and 90 total minutes.

What happens with a skipped or repeated local time?

A time skipped by a clock change is refused rather than moved forward. A time that occurs twice is also refused because this page has no UTC-offset selector. Choose unambiguous local endpoints. Both endpoints use your device’s current time zone; there are no separate departure and arrival zones for flight calculations.

What does the weekday count include?

Monday–Friday dates from the earlier date, including that date and excluding the later date, regardless of the clock times. A Monday 23:00 to Tuesday 01:00 span has zero whole calendar days but one weekday date. Public holidays are not removed. Use Business Days Calculator for its supported holiday regions and endpoint-inclusion options.

Can I enter seconds or earlier dates?

The inputs support whole seconds and Gregorian years 0001–9999. Milliseconds, leap seconds, year zero and ambiguous non-ISO date formats are refused. Browser time-zone rules supply local UTC offsets; leap seconds and historical calendar reforms are not modeled.

Can the end date be earlier than the start?

Yes. All numbers show the magnitude of the span; the headline says End is before start by. Swap reverses the endpoints. Equal endpoints give zero. This page does not add a duration to a date or subtract lunch breaks; the related Date, Time and Hours calculators serve those tasks.

Are my dates remembered?

Restoration only reads the existing record. Deliberate valid edits save dates in this browser and preserve unknown saved fields. Invalid drafts keep the last saved dates. An unusable saved record is retained until you choose Forget saved dates. Storage refusal does not prevent calculation; nothing is uploaded.

Duration Calculator

Enter two local date/time endpoints to measure their duration. Calendar years, months and days follow the clock face; whole elapsed hours, minutes and seconds use your device’s time-zone rules. The headline shows up to three units, and the complete breakdown shows every unit. For date-only counting, use Date Calculator’s Days Between page.

Pick two momentsBoth dates need a value before we can measure between them.

From

To

Both moments use your device’s local time zone. Whole days and weeks follow the calendar; whole hours, minutes and seconds measure elapsed time. Weekdays count Monday–Friday dates, including the earlier date and excluding the later one, without holidays.

Common questions

How are months and years counted?: Whole months use clamped calendar anniversaries. January 31 to February 28 is one month in a common year; January 31 to March 1 is one month and one day. A February 29 anniversary clamps to February 28 in a common year. Twelve whole months make one year. Whole calendar months combines the year and month parts; no average month length is used.
Why can one calendar day contain 23 or 25 elapsed hours?: Local UTC offsets can change between the endpoints. Midnight to midnight across a spring-forward change can be one calendar day but 23 elapsed hours, and across fall-back it can be 25. Days and weeks count whole clock-face calendar units. Total hours, minutes and seconds are whole elapsed units, rounded down; 90 elapsed minutes shows 1 total hour and 90 total minutes.
What happens with a skipped or repeated local time?: A time skipped by a clock change is refused rather than moved forward. A time that occurs twice is also refused because this page has no UTC-offset selector. Choose unambiguous local endpoints. Both endpoints use your device’s current time zone; there are no separate departure and arrival zones for flight calculations.
What does the weekday count include?: Monday–Friday dates from the earlier date, including that date and excluding the later date, regardless of the clock times. A Monday 23:00 to Tuesday 01:00 span has zero whole calendar days but one weekday date. Public holidays are not removed. Use Business Days Calculator for its supported holiday regions and endpoint-inclusion options.
Can I enter seconds or earlier dates?: The inputs support whole seconds and Gregorian years 0001–9999. Milliseconds, leap seconds, year zero and ambiguous non-ISO date formats are refused. Browser time-zone rules supply local UTC offsets; leap seconds and historical calendar reforms are not modeled.
Can the end date be earlier than the start?: Yes. All numbers show the magnitude of the span; the headline says End is before start by. Swap reverses the endpoints. Equal endpoints give zero. This page does not add a duration to a date or subtract lunch breaks; the related Date, Time and Hours calculators serve those tasks.
Are my dates remembered?: Restoration only reads the existing record. Deliberate valid edits save dates in this browser and preserve unknown saved fields. Invalid drafts keep the last saved dates. An unusable saved record is retained until you choose Forget saved dates. Storage refusal does not prevent calculation; nothing is uploaded.

Gregorian calendar arithmetic with clamped month anniversaries. Elapsed units follow the device’s time-zone rules and are whole units rounded down. Skipped/repeated local endpoints are refused; milliseconds, leap seconds, separate time zones and historical calendar reforms are not modeled. Weekdays exclude weekends only.