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MethodologyAbout

Duration arithmetic

Time Calculator

Add or subtract hours, minutes, and seconds as durations. Negative results stay signed and normalized.

Your numbers

Duration arithmetic

Add or subtract hours, minutes, and seconds. Not a clock and not a date.
h
m
s
h
m
s

Normalized duration

4h 15m 0s
How we got this
  1. Left duration9900 seconds
  2. Right duration5400 seconds
  3. Normalized result4h 15m 0s
What we assumed
  • This is duration arithmetic, not a clock time or a calendar date.
  • Hours, minutes, and seconds are converted to a signed second total, then normalized.
  • A negative result means the second duration was larger than the first when subtracting.
Technical details

Method time-v1.0.0Data Manual inputs / fixed rules

Discrepancy in the numbers? You can click Report incorrect result below or email hello@costanswer.com with the Method and Data lines.

Guide

Duration arithmetic, not clock times in a time zone

CostAnswer editorialIndependent calculator publisher

Add or subtract hours, minutes, and seconds as durations. Negative results stay signed and normalized. This is not a world-clock converter and not a timesheet.

Normalized output

90 minutes becomes 1 hour 30 minutes in the display. The engine keeps SI-style sexagesimal normalization so the parts stay in range.

Questions about this calculator

Can I subtract two clock times?

Convert each to a duration from midnight first, or use the time-card calculator for shifts. This page adds durations, not “3:15 PM minus 11:40 AM” as civil times.

Can I add hours across midnight?

You are adding durations, not civil clock times. For a shift that crosses midnight, use the time-card calculator.

Terms used here

Duration
A length of time, not a timestamp on a calendar.

Practical tips

For overnight shifts, time-card is the right tool.

Limits and caveats

Exact duration math. Not a timezone or DST engine.

Results are for information. They are not legal, tax, medical, or financial advice. How the math is maintained · Report a wrong figure.

Engine notes

Rounding, versioning, and omissions that sit beside the guide rather than repeating it.

  • Seconds first. Hours, minutes, and seconds become a signed second total, then the result is normalized.
  • Negatives. Subtracting a larger duration from a smaller one keeps a minus sign. It does not wrap a 24-hour clock.
  • Not a timesheet. Shift start and end belong on the Time Card calculator.

Calculation receipt

What each number here is

This answer is arithmetic on what you enter. No outside dataset is involved, so nothing here can go out of date.

Time arithmetic is defined by the units.

Next

People working through dates and hours usually need these next.

EverydayTime cardAdd shift start, end, and unpaid break across one or more days, including overnight shifts. Overtime law is not applied.EverydayDate offsetFind the calendar date a given number of days, weeks, months, or years before or after another date. Month ends are clamped.EverydayDays from todayThe calendar date that is N days from today, or N days ago. Weekends still count; this is not business days.EverydayBusiness daysCount workdays between two dates, or add workdays to a date. Federal holidays are optional.EverydayPer diemFederal travel per diem for a trip in the continental U.S.: the GSA lodging ceiling for every night, meals and incidentals for every day, and a check of your actual room rate against the cap. Type a city or ZIP.EverydayAgeCompleted years, months, and days from a birth date to a selected as-of date, including leap-day rules.