Time Calculator

The everyday time toolkit: find how far apart two clock times are, add or subtract hours and minutes from a time, or convert a duration between seconds, minutes, hours, days, and weeks — all worked out step by step.

For personal planning and general reference — verify important results when needed.

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Format: HH:MM or HH:MM:SS (24h)

Select a calculation type, enter your values, and click Calculate to see results with step-by-step solution.

Finding the gap between two clock times

Subtracting one clock time from another looks simple until the times don't line up on clean hour boundaries — time doesn't carry in base 10, it carries in base 60, so 9:45 to 11:20 isn't just "11.20 minus 9.45."

9:45 to 11:20 → borrow 60 minutes from the hour

11:20 = 10:80 → 10:80 − 9:45 = 1 hour 35 minutes

That borrowing step is exactly where manual time math goes wrong most often — this calculator's Time Difference mode does the borrowing automatically and shows the working, so it's easy to see where each figure came from.

Adding and subtracting across midnight

A clock resets to 0:00 every 24 hours, but elapsed time doesn't care about that reset — a shift or trip that starts at 22:00 and runs 9 hours ends at 7:00 the next morning, not at a nonsensical "31:00." The Add/Subtract mode here handles that wraparound automatically: add the hours and minutes, then loop back to 0:00 (and roll the day count forward) whenever the total reaches 24:00. It's the same logic used for overnight shift scheduling, flight arrival times, or any calculation that starts on one day and lands on the next.

Why decimal time and clock time need separate conversion

45 minutes looks like "0.45" if you're not careful, but it's actually 0.75 of an hour — the base-60 to base-10 switch trips people up constantly, especially anywhere billing or payroll is involved.

Decimal hours = Hours + (Minutes ÷ 60)

1 hour 45 minutes = 1 + (45 ÷ 60) = 1.75 hours

The Convert Units mode moves between seconds, minutes, hours, days, and weeks directly, which covers this conversion along with the more general case of converting any duration into whatever unit a form, spreadsheet, or invoice happens to want.

More specialized time tools

For payroll specifically — regular hours, overtime, and a full weekly timecard — the time card calculator and the hours calculator go deeper than this general-purpose tool. For measuring how long a single event, task, or activity lasted, the time duration calculator is built specifically for that.

Frequently Asked Questions

What operations can a time calculator perform?

Add or subtract hours, minutes, and seconds; find elapsed time between clock times; and convert between decimal hours and HH:MM:SS formats.

How do you add times that exceed 24 hours?

Sum hours normally — 30 hours total is valid for elapsed-duration work even though a clock wraps every 24 hours.

What is decimal time used for?

Billing and payroll often express 90 minutes as 1.5 hours. Converting HH:MM to decimal prevents rounding errors in invoices.

How does crossing midnight affect calculations?

When end time is before start time on a clock, add 24 hours to the end time to get correct elapsed duration for overnight periods.

How do I use this time calculator?

Choose add, subtract, or convert mode, enter times in HH:MM or decimal form, and click Calculate. Results show in your selected format.

How do I add hours to a time that rolls past midnight?

Add the hours and minutes normally, then subtract 24 hours from the result whenever it reaches 24:00 or beyond. Starting at 22:00 and adding 5 hours gives 27:00, which becomes 3:00 the next day once the 24-hour wrap is applied.

Why use 24-hour time instead of AM/PM?

A 24-hour clock removes the AM/PM ambiguity entirely, and it makes arithmetic simpler since every hour of the day has one unique number. 14:00 is unambiguously 2 PM, with no risk of misreading it as the other half of the day the way a bare "2:00" can be.

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