How do I add two times together?

In the "Add / Subtract Time" tab, enter each time as days, hours, minutes, and seconds, choose add or subtract, and the calculator returns the combined time normalized to days, hours, minutes, and seconds — for example 2h 45m + 1h 30m = 4 hours, 15 minutes.

What happens if subtracting gives a negative time?

The result is shown with a minus sign. Subtracting a larger time from a smaller one yields a negative span, such as 1h − 90m = −30 minutes.

How does adding time to a date work?

In the "Add / Subtract to a Date" tab, enter a start date and a time of day (24-hour), then the days, hours, minutes, and seconds to add or subtract. The calculator rolls the time over across midnight and returns the resulting date, time, and day of the week.

What is the time expression format?

The "Time Expression" tab evaluates a string using d, h, m, and s with + and − operators, like "1d 2h 3m 4s + 4h 5s - 2030s + 28h". Each value group is summed according to the operator before it.

How many seconds are in a day, hour, and minute?

A day is 86,400 seconds, an hour is 3,600 seconds, and a minute is 60 seconds. All time arithmetic here is done by converting to seconds and back.

Should I use this calculator to find the time between two clock times?

Use the Time Duration Calculator for an elapsed interval between clock times or dated timestamps. This calculator adds or subtracts time spans.

Does adding time to a date account for daylight saving time?

No. Each day is treated as exactly 24 hours. The calculator has no time zone, so use a time-zone-aware tool when a daylight-saving change matters.

Time Calculator — Add & Subtract Time

Add and subtract time three ways: combine two day/hour/minute/second values, apply a span to a starting date and time, or evaluate a free-form time expression. Every result is normalized to days, hours, minutes, and seconds (and shown in total hours, minutes, and seconds).

Add hours, minutes, and seconds

Enter the first span in Time 1 and the second in Time 2, then choose Add or Subtract. Leave unused units at zero. The calculator converts both spans to seconds before doing the arithmetic, so values such as 90 minutes are carried into hours automatically.

Task	Enter	Result
Add time	2 hours 45 minutes + 1 hour 30 minutes	4 hours 15 minutes
Subtract time	1 hour 10 minutes − 45 minutes	25 minutes
Carry past a day	23 hours 30 minutes + 2 hours	1 day 1 hour 30 minutes

For the first row, 45 + 30 = 75 minutes, or 1 hour 15 minutes; adding the remaining hours gives 4 hours 15 minutes. For the second, borrowing an hour turns 1 hour 10 minutes into 70 minutes, and 70 − 45 = 25 minutes.

If you have two clock readings and need the elapsed interval between them, use the Time Duration Calculator. For work shifts with breaks, use the Time Card Calculator.

Time units

Unit	Seconds
1 minute	60
1 hour	3,600
1 day	86,400
1 week	604,800

Examples

Add two times

2 days 5 hours 30 minutes plus 1 day 20 hours 45 minutes equals 4 days, 2 hours, 15 minutes (353,700 seconds).

Evaluate an expression

"1d 2h 3m 4s + 4h 5s - 2030s + 28h" totals 206,959 seconds, which is 2 days, 9 hours, 29 minutes, 19 seconds.

Add time to a date

Starting at 12:00:00 on June 17, 2026 and adding 30 hours gives 18:00:00 on Thursday, June 18, 2026.

Formula

All modes convert each value to seconds, apply the operations, then normalize back:

total seconds = days×86,400 + hours×3,600 + minutes×60 + seconds
days = ⌊total ÷ 86,400⌋   hours = ⌊remainder ÷ 3,600⌋
minutes = ⌊remainder ÷ 60⌋   seconds = remainder

For a date, the start date and time of day become seconds since a reference day; adding the span and converting back gives the new date and clock time.

Date arithmetic treats every calendar day as 24 hours. It does not model time zones or daylight-saving transitions.

In the expression tab, an operator applies to the whole value group that follows it: "1d 2h - 30m" adds a day and two hours, then subtracts 30 minutes.

Lab timepoint worksheet: a 40-hour interval

Suppose an incubation starts at 3:00 PM on Monday, October 5, 2026 and the next observation is due 40 hours later. In Add / Subtract to a Date, enter the start date, use 15 for the 24-hour start hour, and add 40 hours.

Break the check at midnight:

Step	Elapsed time	Clock time
Monday 3:00 PM to midnight	9 hours	Tuesday 12:00 AM
One full day	24 hours	Wednesday 12:00 AM
Remaining interval	7 hours	Wednesday 7:00 AM

The 40-hour timepoint is Wednesday, October 7, 2026 at 07:00:00. Record the start timestamp, interval, and result together so another person can reproduce the schedule. This example assumes continuous elapsed time: it does not skip weekends or lab-closed hours. Because the calculator treats every day as 24 hours, use a time-zone-aware scheduling system if an interval crosses a daylight-saving transition.

Clock hours or calendar dates?

For one start/end shift and an unpaid break, use the Hours Calculator. For a span measured in calendar years, months, or days, use the Date Calculator. Choose the tool before converting months to days: calendar months have different lengths.

Time Calculator

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