Time Addition & Subtraction Calculator

Add and subtract durations in days, hours, minutes and seconds, or add and subtract time from a clock time. Use as many rows as you need, see a step-by-step breakdown and a normalised result, including day offsets such as “next day” or “+2 days”.

Date & Time Runs client-side Free to use

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About the Time Addition & Subtraction Calculator

Time Addition & Subtraction Calculator works with elapsed time. In duration mode, add and subtract any number of rows of days, hours, minutes and seconds to get a total such as 1 day 2 h 15 min 30 s, also shown in seconds, minutes and hours. In clock-time mode, start from a time of day such as 22:45 and add or subtract durations to find the resulting time and how many days it moves, such as “next day”, “previous day” or “+2 days”.

Each row has its own add or subtract choice, so all values are entered as whole, non-negative numbers; values carry over automatically (90 minutes becomes 1 h 30 min) and borrowing across seconds, minutes, hours and days is handled for you. A breakdown shows each row in seconds and the normalised result. This is elapsed time only: it does not convert time zones or apply daylight-saving changes, and clock results assume 24-hour days.

How to use

Choose duration mode or clock-time mode.
In clock-time mode, enter the starting time.
Enter durations in the rows and choose + or − for each.
Add or remove rows as needed, then press Calculate.
Copy or download the summary.

Key features

Two modes: durations, or a clock time plus durations.
Days, hours, minutes and seconds in every row.
Up to 50 editable rows with add and remove.
Automatic carrying and borrowing.
Day offsets such as next day, previous day or +2 days.
Step-by-step breakdown and normalised result.
Copy Summary and Download Summary.

Best practices

Use the − option to subtract rather than typing negative numbers.
Check the breakdown to confirm each row.
Use clock-time mode for shift ends or travel arrival times.
Use a time zone converter when locations differ.
Remember daylight-saving changes are not applied.

Benefits

Fast, error-free time arithmetic.
Clear day offsets for clock times.
Transparent working you can check.
Private: nothing is uploaded or stored.

Frequently asked questions

How do I subtract time?

Choose − Subtract on the row. All fields take whole, non-negative numbers; the row’s operation decides whether it is added or taken away.

Can I enter 90 minutes?

Yes. Values carry over automatically, so 90 minutes is treated as 1 hour 30 minutes in the result.

What does the day offset mean?

In clock-time mode it shows how many midnights the result crosses: same day, next day (+1 day), previous day (−1 day), or a number of days.

Does it handle time zones or daylight saving?

No. It adds and subtracts elapsed time only and assumes every day has 24 hours. Use a time zone converter for different locations.

Can the total be negative?

In duration mode, yes — if you subtract more than you add, the total is shown with a minus sign. In clock-time mode a negative change moves the time earlier, possibly to a previous day.

What are the limits?

Up to 50 rows, and each value and the total must stay within about 100 years.

Is anything saved or sent anywhere?

No. Everything runs in your browser. Times, laps, shifts, events and dates are not uploaded and are not saved in browser storage. Reset clears them, and closing the page discards them.