acalculator

How do I add or subtract times?

Add or subtract two durations, such as 2 h 45 min 30 s plus 1 h 30 min 45 s. Or switch modes to add time to a clock time and date.

Your numbers

Add or subtract?
Result
4 hours, 16 minutes, 15 seconds

The answer is 4 hours, 16 minutes, 15 seconds.

In days
0.177951
In hours
4.2708
In minutes
256.25
In seconds
15,375

Answer for the example date Tuesday, September 29, 2026. It changes to today's date when the page loads.

Result: 4 hours, 16 minutes, 15 seconds. The answer is 4 hours, 16 minutes, 15 seconds.

How to calculate

Adds or subtracts two durations in days, hours, minutes, and seconds, or adds or subtracts a duration from a date and time of day.

Example with the default inputs (What do you want to do? Add or subtract durations, Hours (first duration) 2, Minutes (first duration) 45, Seconds (first duration) 30, Add or subtract? Add +, Hours to add or subtract 1, Minutes to add or subtract 30, Seconds to add or subtract 45) on the example date Tuesday, September 29, 2026: The answer is 4 hours, 16 minutes, 15 seconds.

Method: Two durations: seconds = days × 86,400 + hours × 3,600 + minutes × 60 + seconds for each, then add or subtract and split back into days, hours, minutes, and seconds. From a date and time: move the start by the duration in seconds.

  • Every day has 24 hours: daylight saving clock changes and leap seconds are not counted.
  • Empty boxes count as 0. Decimals are allowed (1.5 hours is 1 hour 30 minutes).
  • A subtraction that goes below 0 gives a negative duration, shown with a minus sign.
  • The seconds are added or subtracted unrounded, then rounded once: a duration result to the millisecond, a date and time result to the nearest second. A seconds part of the start time is kept.

Machine-readable copies: Markdown, JSON.

Worked examples

Each example is checked against the calculator on every build.

  1. What do you want to do? Add or subtract durations, Hours (first duration) 2, Minutes (first duration) 45, Seconds (first duration) 30, Add or subtract? Add +, Hours to add or subtract 1, Minutes to add or subtract 30, Seconds to add or subtract 45 gives Result 4 hours, 16 minutes, 15 seconds, In seconds 15,375, In minutes 256.25.Source: hand calculation in content.mdx: 30 + 45 = 75 s = 1 min 15 s; 45 + 30 + 1 = 76 min = 1 h 16 min; 2 + 1 + 1 = 4 h
  2. What do you want to do? Add or subtract durations, Days (first duration) 1, Hours (first duration) 3, Add or subtract? Subtract −, Hours to add or subtract 5, Minutes to add or subtract 20 gives Result 21 hours, 40 minutes, In hours 21.666667.Source: hand calculation in content.mdx: 27 h − 5 h 20 min = 21 h 40 min
  3. What do you want to do? Add or subtract durations, Minutes (first duration) 90, Add or subtract? Subtract −, Hours to add or subtract 2 gives Result -30 minutes, In seconds -1,800.Source: hand calculation in content.mdx: 90 min − 120 min = −30 min
  4. What do you want to do? Add or subtract durations, Hours (first duration) 1.5, Add or subtract? Add +, Minutes to add or subtract 0.25 gives Result 1 hour, 30 minutes, 15 seconds, In seconds 5,415.Source: hand calculation in content.mdx: 1.5 h = 5,400 s; 0.25 min = 15 s
  5. What do you want to do? Change a date and time, Start date 2026-09-27, Start time 22:30:00, Add or subtract? Add +, Hours to add or subtract 8, Minutes to add or subtract 45 gives Result Monday, September 28, 2026, 7:15:00 AM, Date 2026-09-28, Time 07:15:00.Source: hand calculation in content.mdx: 22:30 + 8:45 = 31:15, which is 7:15 the next day
  6. What do you want to do? Change a date and time, Start date 2026-03-01, Start time 06:00:00, Add or subtract? Subtract −, Days to add or subtract 1, Hours to add or subtract 7 gives Date 2026-02-27, Time 23:00:00.Source: hand calculation in content.mdx: back 1 day to February 28, 6:00 AM, then 7 hours to 11:00 PM on February 27

How it works

Two durations

Each duration becomes seconds:

seconds = days × 86,400 + hours × 3,600 + minutes × 60 + seconds

The two are added or subtracted without rounding, and only the result is rounded, once, to the millisecond. So 0.0004 s + 0.0004 s is 0.001 seconds, and 1.0006 s − 0.0004 s is 1 second. The result is split back into parts:

  • days = seconds ÷ 86,400, rounded down
  • hours = what is left ÷ 3,600, rounded down
  • minutes = what is left ÷ 60, rounded down
  • seconds = what is left

A negative result is shown with a minus sign in front of all its parts. The totals are the result in days, hours (÷ 3,600), minutes (÷ 60), and seconds.

From a date and time

The start date and time become seconds since January 1, 1970, 00:00:00 (days × 86,400 plus the time of day). The duration in seconds (not rounded) is added or subtracted, the result is rounded once to the nearest second (11:00:00 plus 0.4996 s is 11:00:00), and it becomes a date and a time of day again. Crossing midnight moves the date.

Assumptions

  • Every day is 24 hours. Daylight saving clock changes and leap seconds are not counted.
  • Empty boxes are 0. Boxes take decimals from 0 up to 100,000 days, 1,000,000 hours, 10,000,000 minutes, or 1,000,000,000 seconds.
  • Start dates are on the Gregorian calendar, from 1600 to 2400. A result past those years still shows (the durations can carry it to about 1160 or 2840).

Worked examples by hand

2 h 45 min 30 s + 1 h 30 min 45 s. Seconds: 30 + 45 = 75 = 1 minute 15 seconds. Minutes: 45 + 30 + 1 = 76 = 1 hour 16 minutes. Hours: 2 + 1 + 1 = 4. Answer: 4 hours, 16 minutes, 15 seconds, which is 15,375 seconds or 256.25 minutes.

1 day 3 hours − 5 hours 20 minutes. 1 day 3 hours is 27 hours. 27 h − 5 h 20 min = 21 hours, 40 minutes, or 21.6667 hours.

90 minutes − 2 hours. 90 − 120 = −30 minutes (−1,800 seconds).

1.5 hours + 0.25 minutes. 1.5 × 3,600 = 5,400 seconds; 0.25 × 60 = 15 seconds. Total 5,415 seconds: 1 hour, 30 minutes, 15 seconds.

10:30 PM on September 27, 2026, plus 8 hours 45 minutes. 22:30 + 8:45 = 31:15. Take off 24 hours for the next day: Monday, September 28, 2026, 7:15 AM.

6:00 AM on March 1, 2026, minus 1 day 7 hours. Back 1 day is 6:00 AM on February 28 (2026 is not a leap year). Back 7 more hours crosses midnight: 11:00 PM on February 27, 2026.

Other questions people ask

How do I add hours and minutes?

Add each unit on its own, then carry: 60 seconds make a minute, 60 minutes make an hour, and 24 hours make a day. 2:45:30 plus 1:30:45 is 75 seconds (1 minute 15 seconds), 76 minutes (1 hour 16 minutes), and 4 hours: 4 hours, 16 minutes, 15 seconds.

How do I subtract time?

Subtract each unit, borrowing from the next unit up when you run short. 1 day 3 hours minus 5 hours 20 minutes: borrow 1 hour for 60 minutes, so 60 − 20 = 40 minutes, then 26 − 5 = 21 hours: 21 hours 40 minutes. If the second time is longer, the answer is negative.

What time will it be 8 hours and 45 minutes from 10:30 PM?

22:30 + 8:45 = 31:15 on a 24-hour clock. That is past 24:00, so it is the next day at 7:15 AM. Pick "Change a date and time" to get the date too.

Can I use decimals?

Yes. 1.5 hours is 1 hour 30 minutes, and 0.25 minutes is 15 seconds. Empty boxes count as 0.

How do I convert the result to hours or minutes?

The page shows the total in days, hours, minutes, and seconds. 4 hours 16 minutes 15 seconds is 15,375 seconds, 256.25 minutes, or 4.2708 hours.

Does it count daylight saving time?

No. Every day is 24 hours of clock time. If you add time across a clock change, the real time is an hour off the clock time shown.