Time Calculator

About this tool

This calculator handles two jobs that regular calculators get wrong because time isn't base-10. The Add / Subtract tab adds or subtracts two durations entered as hours, minutes, and seconds, carrying correctly at 60. The Duration tab takes a start and end clock time (with AM/PM) and tells you the elapsed time between them — and if the end time is earlier than the start, it assumes you crossed midnight and wraps around. Everything runs locally in your browser; nothing you enter is sent or stored.

Results show the answer in hours, minutes, and seconds, plus the total in raw seconds and decimal minutes or hours — handy when a timesheet or invoice wants "7.75 hours" instead of "7h 45m". Press Enter anywhere to calculate, and Reset clears the active tab.

When to use it

• Totaling worked hours for a timesheet, including overnight shifts that cross midnight.
• Adding up split times — workout intervals, audio or video segment lengths, cooking stages.
• Converting a duration like 2h 21m into decimal hours for billing or payroll.

A worked example

Say you edited two video clips, one 1:45:30 long and one 2:30:45. Adding them by hand, the seconds come to 75 — that's 1 minute 15 seconds, so you carry one minute. The minutes then total 76, so you carry an hour. The result is 4h 16m 15s, which this tool computes instantly (15,375 seconds, or 256.25 minutes). The same carry logic is why 9:00 AM to 5:30 PM comes out to 8h 30m on the Duration tab, and why a 10:00 PM to 6:00 AM shift correctly reads 8h 00m instead of a negative number.

Frequently asked questions

How do overnight shifts work on the Duration tab?

If the end time is earlier than the start time, the calculator assumes the end falls on the next day and adds 24 hours. So 11:00 PM to 7:00 AM gives 8h 00m. It always measures forward from start to end within one day-wrap.

Can the result be negative?

On the Add / Subtract tab, yes — subtracting a larger duration from a smaller one shows a minus sign, which is useful for "how far short am I" questions. The Duration tab never goes negative because it wraps past midnight instead.

How do I convert time to decimal hours?

Run any calculation and read the detail line under the result — it includes the total in decimal form. The math is minutes divided by 60: 45 minutes is 0.75 hours, so 7h 45m equals 7.75 hours.

Does this account for time zones or daylight saving?

No. It does pure clock arithmetic on the numbers you enter. For a duration that spans a daylight-saving change or two time zones, convert both times to one zone (or UTC) first, then enter them here.