Add or subtract days, hours, minutes and seconds with this online time calculator. Choose Duration to combine two lengths of time, Date to move a starting date and clock time, or Expression to calculate a formula such as 2h + 45m – 30s.

Choose the right calculation mode

Use Duration for tasks such as adding study sessions or subtracting a break from a known shift length. Use Date when you have a starting calendar date and clock time. Use Expression when you prefer to type time values and plus or minus operators in one line.

For example, 2h 45m + 1h 30m equals 4 hours 15 minutes. The calculator carries seconds into minutes and minutes into hours. In Duration and Expression modes, 24 hours becomes 1 day.

For date shifts, remember that one calendar day can differ from 24 elapsed hours across daylight saving changes. Check your device time zone before relying on a date result.

Follow the step-by-step guide, read the FAQ, or report a calculation issue.

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A duration is not a decimal

Time rolls over at 60 and at 24, not at 10. Ninety seconds is one minute and thirty seconds. Ninety minutes is one hour and thirty minutes. Twenty-five hours is one day and one hour. The duration calculator carries those units for you. Either row can be left blank, and a blank field is zero.

Use Add when the second time should be joined to the first. Use Subtract when it should be taken away. If the second time is longer than the first, the result is negative.

Shifting a date

The date calculator starts from a calendar day and a clock time, then moves by the amount you enter. A day changes the date and keeps the clock time. Hours, minutes, and seconds are exact lengths, so they can cross midnight. That split matters where daylight saving time is observed: a calendar day is not always 24 hours on the clock.

Leap days and short months are included. 31 January plus one day is 1 February. 28 February 2023 plus one day is 1 March, and 28 February 2024 plus one day is 29 February.

Expressions

An expression is a line of time values with plus and minus. Every number needs a unit. A minus in front of a group applies to each unit in that group, so 2h – 90m is thirty minutes. Decimals are allowed: 1.5h is one hour and thirty minutes. The worked example 1d 2h 3m 4s + 4h 5s – 2030s + 28h equals 2 days, 9 hours, 29 minutes, and 19 seconds.

• d means days
• h means hours
• m means minutes
• s means seconds

Units of time

A week is 7 days. An hour is exactly 3,600 seconds, and a minute is exactly 60 seconds. The second is the SI base unit of time. A common year has 365 days and a leap year has 366. The Gregorian calendar averages 365.2425 days in a year, because 97 years in every 400 are leap years.

The clock still counts by sixties because 60 divides cleanly into halves, thirds, quarters, fifths, and sixths. An hour can be split into 30, 20, 15, 12, 10, 6, 5, 4, 3, or 2 minutes without a remainder.

Unit	Length
Millennium	1,000 years
Century	100 years
Decade	10 years
Gregorian year, average	365.2425 days
Common year	365 days
Leap year	366 days
Quarter	3 months
Month	28 to 31 days
Week	7 days
Day	24 hours, 1,440 minutes, or 86,400 seconds
Hour	60 minutes, or 3,600 seconds
Minute	60 seconds
Second	SI base unit
Millisecond	0.001 seconds