Date & Time Duration Calculator

What this calculator does

The calculator measures the gap between two moments and reports it in the units people actually ask about: full years, full months, full weeks and full days, followed by hours, minutes and seconds. It has two modes, picked with the Select tool choice at the top.

• Date duration calculator takes a start date and an end date, each with an optional time of day. Use it for "how long until", "how long since" and "how long did it take" questions that span days, weeks or years.
• Time duration takes two clock times and gives the difference in hours, minutes and seconds. Use it for a meeting, a shift or a lap that starts and ends on the same day.

How to use it

Date duration. Enter a start date and an end date. Add a time next to either one if the hour matters; an empty time counts as midnight. An empty start or end date means today, which makes the common cases quick: enter only an end date to see the time left until an event, or only a start date to see the time that has passed since one.

Time duration. Enter the From and Until times. Both are required. The two times are compared on a single day, so an Until time earlier than the From time gives a negative answer instead of wrapping past midnight. For a span that crosses midnight, switch to the date mode and put the real dates in.

In date mode the result lists only the units that are not zero: full years, months and weeks disappear while they are still 0, but the full days line always stays. If the end moment is earlier than the start, the hour, minute and second figures turn negative and the year, month, week and day figures describe the size of the gap.

How each unit is counted

• Full years and months are counted on the calendar from the start moment. A month is added to the start date at a time, so it keeps the same day of the month. When that day does not exist in the target month (31 January plus one month), the date rolls forward into the following month, so the month only counts as complete once the end moment reaches that rolled date.
• Full days is the elapsed time divided by 24 hours, rounded down. Starting at 09:00 and ending at 08:00 two days later is 1 full day, not 2.
• Full weeks is the full days divided by 7, rounded down.
• Hours (decimal), hours and minutes and minutes and seconds describe the whole span, not a remainder.

total hours = full days × 24 + leftover hours + leftover minutes ÷ 60

Worked examples

A project from start to finish. Work begins on 12 March 2026 at 09:00 and ends on 28 April 2026 at 17:30. The calendar gap from 12 March to 28 April is 47 days, and the clock adds 8 hours 30 minutes, so the total is 47 × 24 + 8.5 = 1,136.5 hours. The calculator shows 1 full month (12 March to 12 April), 6 full weeks, 47 full days, 1,136 hours and 30 minutes, and 68,190 minutes (4,091,400 seconds).

A working session. Time duration from 09:45 to 16:20 is 6 hours 35 minutes, which is 395 minutes, 23,700 seconds or 6.58 decimal hours.

An overnight journey. A coach leaves at 21:15 on 3 November 2026 and arrives at 06:40 on 5 November. Entered in date mode, the span is 33 hours 25 minutes: 1 full day, with 2,005 minutes in total. The same two clock times in time duration mode would give a misleading negative answer, because that mode does not know a day has passed.

Time left until or since an event. Leave the start date empty and enter a future end date to count down to it, or enter a past start date and leave the end date empty to count up from it. If you only need whole days, the day counter and the days calculator give a shorter answer, and the working days calculator leaves out weekends.

Time zones, daylight saving and leap seconds

The calculator works on the wall-clock values you type. It does not know which time zone either moment belongs to and it does not adjust for daylight saving changes. If the clocks moved between the two moments, the true elapsed time can differ from the figure shown by one hour. To compare moments in different places, first translate both to the same zone with the time zone converter.

Leap seconds are ignored as well. They were added to civil time 27 times between 1972 and 2016 to keep it close to the Earth's rotation, and international bodies have agreed to stop adding them. Every day here is exactly 86,400 seconds, which is accurate for scheduling, billing and planning.