Time Calculator

How to work it out yourself

1. 1.Enter each duration in hours, minutes and seconds. Leave a field at zero rather than converting it yourself.
2. 2.Time carries in sixties, not tens, which is why adding 45 and 20 minutes gives 1:05 and not 65. Converting to seconds first and back at the end removes the carry entirely.
3. 3.Read the decimal hours line before typing anything into payroll or an invoice. 6:05 is 6.0833 hours, not 6.05, and the difference compounds over a month.

The formula

1. First duration in secondsh1 * 3600 + m1 * 60 + s1
2. Second duration in secondsh2 * 3600 + m2 * 60 + s2
3. Result in secondsoperation_add * (first + second) + operation_subtract * (first - second)
4. As a clock readingtotal
5. Whole hoursfix(abs(total) / 3600) * sign(total)
6. Minutes past the hourfloor(mod(abs(total), 3600) / 60)
7. Seconds past the minutemod(abs(total), 60)
8. Decimal hourstotal / 3600
9. Total minutestotal / 60
10. In days and hourstotal / 86400

Source: BIPM SI Brochure — the second, and units accepted for use with the SI, US Department of Labor, 29 CFR 785.48 — recording and rounding working time

Questions people actually ask

Why is 6:05 not 6.05 hours?

Because minutes are sixtieths of an hour, not hundredths. Five minutes is 5/60 of an hour, which is 0.0833, so 6:05 is 6.0833 hours. Reading the clock straight into a decimal field understates every entry whose minutes are under 60 and is the commonest timesheet error there is.

Can the result be negative?

Yes, and it is shown as one. Subtracting a longer duration from a shorter one is a real question — how much short a session ran, how far past a budget — and hiding the sign would turn a deficit into a surplus.

How is this different from the hours worked calculator?

That one takes clock-in and clock-out times, handles a break and applies a rounding policy, which is a timesheet. This one adds and subtracts bare durations, which is what you want for stacking session lengths, splitting a budget, or checking a total.

Does it handle durations over 24 hours?

Yes. The clock reading keeps counting rather than wrapping, so 30 hours reads as 30:00:00 and not 6:00:00, and the days line is there when that is the more useful shape.

Related

• Hours CalculatorHours worked between two times, less breaks, in decimal payroll hours — with what the federal rounding rules do to the total.
• Date CalculatorWhat date falls a given number of days or weeks from another date, counting calendar days or business days.
• Age CalculatorExact age in years, months and days from a birth date, plus the total days lived and the next birthday.
• Percentage Change CalculatorPercentage increase or decrease between two values, with the absolute difference and the multiplier.