Time Calculator

// Time is base 60, and your keyboard is not

Two hours forty-five minutes plus one hour thirty is four hours fifteen — 4.25 hours in decimal — and not 4.15, which is what reading the colon as a decimal point gives you. Minutes roll over at sixty rather than at a hundred, so every column carries at a different point from the arithmetic you learned for money. That single mismatch is why people search for a calculator to do a sum they could otherwise do in their head.

The add-and-subtract mode works the way an adding machine tape does. Each row is one duration, typed the way you already write them — 2:45, 2h 45m, or 90m — and the total updates on every keystroke; a row you flip to minus is subtracted rather than removed, so the tape still shows what you took off. Every row echoes back what it understood, and overflowing a unit is fine on purpose — 90 minutes reads as an hour and a half, because that is what 90 minutes is, and rejecting it would be a form being fussy about a number that is perfectly valid.

Totals are not wrapped at 24 hours either. Thirteen shifts of two hours is 26:00:00, not 2:00:00 the following day. A running total that silently wraps is the kind of wrong answer nobody catches, because it looks exactly like a right one.

// Hours worked, and why payroll wants 7.5 instead of 7:30

Timesheets, invoices, and payroll systems multiply hours by a rate, and 7:30 cannot be multiplied — the colon is a separator, not a decimal point. Seven hours thirty minutes billed as 7.30 hours is seven hours and eighteen minutes, so every entry loses twelve minutes. The conversion is division by sixty: thirty minutes is 0.5 of an hour, fifteen minutes is 0.25, forty-five minutes is 0.75, and twenty minutes is the recurring 0.333… that gets written as 0.33.

Every result on this page carries a decimal-hours row for exactly that reason, rounded to two decimals — the precision payroll software actually stores — while the underlying arithmetic stays in whole seconds. Rounding happens once, at the moment of display, so a long tape of entries does not accumulate the drift you get from rounding each line before adding it.

The rounding is half away from zero on the exact value, not on the floating-point approximation of it. One hour and eighteen seconds is precisely 1.005 hours; the obvious implementation returns 1.00, because the binary form of 1.005 sits a hair below the halfway point. It is a small error, and it is a small error that shows up on a payslip.

// Shifts that cross midnight

Eleven at night to half past six in the morning is seven and a half hours, but subtracting one clock time from the other gives minus sixteen and a half. That is the single most common failure in hours arithmetic, and it is why so many pages ranking for this query are payroll blogs explaining the workaround by hand.

When the end time is earlier than the start and no dates are involved, this tool reads it as the next day and says so on screen — the assumption is written out, not applied quietly. Tools that fix it silently are right most of the time and impossible to check the rest of the time.

When a span really does cover more than one night, switch on the two date fields. With dates present nothing is assumed: an end that falls before the start is reported as an error rather than reinterpreted, because the visitor has told the tool exactly what they meant and the only remaining explanation is a mistake.

// What this measures, and what it does not

This is wall-clock arithmetic. Nine in the morning on the Saturday of a daylight-saving weekend to nine the next morning, with both dates filled in, is counted as 24 hours, because that is what the two clock faces say and what the question usually means. The elapsed physical time is 23 or 25 hours depending on the direction of the change, and if that distinction matters — flight times, server uptime, anything measured in real elapsed seconds — this is not the right instrument.

The arithmetic never builds a calendar date object or consults a time zone database — the date boxes are read as plain year-month-day text — which is precisely how the daylight-saving answer above stays predictable. Dated spans are counted as whole calendar days between the two dates plus the difference between the two clock times, on the proleptic Gregorian calendar, leap years included.

Clock times are read at minute resolution in the between-two-times mode and accept the shapes people actually type: 5:30 PM, 17:30, 530pm, or a bare 9. Anything it cannot read is marked rather than guessed at, because a start time silently parsed as the wrong half of the day produces a duration that is confidently, invisibly twelve hours out.

// fair questions

How do you add hours and minutes together?

Add the minutes first, and every time they pass 60, carry an hour. 2:45 plus 1:30 gives 75 minutes, which is one hour and 15 minutes, so the answer is 4:15. The add-and-subtract mode above does the carrying for you and updates as you type, including when a row is set to subtract.

How do I calculate hours worked between two times?

Switch to "Between two times", enter the clock-in and clock-out times, and read the total. The result panel gives it as hours:minutes:seconds, as total minutes, and as decimal hours — the last one is what a timesheet or invoice usually wants.

What is 7 hours and 30 minutes in decimal?

7.5 hours. Divide the minutes by 60 and add them to the hours: 30 ÷ 60 = 0.5. The common ones are 15 minutes = 0.25, 20 minutes = 0.33, 30 minutes = 0.5, and 45 minutes = 0.75. Writing 7:30 as 7.30 on an invoice is the classic error — 7.30 hours is 7 hours 18 minutes, so it undercharges by 12 minutes.

How does the calculator handle overnight shifts past midnight?

If the end time is earlier than the start time and you have not entered dates, it counts through midnight to the next day and tells you it has done so. 11:00 PM to 6:30 AM comes out as 7 h 30 m. If you want a span across specific days instead, tick "These times are on different days" and set both dates — then nothing is assumed.

Does it handle daylight saving time?

It measures the clock, not elapsed physical time. A span from 9:00 AM one day to 9:00 AM the next — with the two date fields switched on — reads as 24 hours even across a daylight-saving change, when the real elapsed time is 23 or 25 hours. That is the right answer for shifts and schedules, and the wrong one for anything measured in true elapsed seconds.

Can I enter times in 24-hour or military format?

Yes. 17:30, 1730, 5:30 PM and 530pm are all read as half past five in the afternoon, and a bare 9 is read as nine o'clock. Each field says back which time it heard, and the AM/PM / 24-hour toggle shows every result in whichever convention you read — it starts on 24-hour time unless your device is set to a US locale.

Do my times leave this page?

No. Every calculation runs in your browser as you type. Nothing you type is uploaded, stored, or logged, and the page keeps working with the network disconnected.