Time Duration Calculator

Calculate duration between times, add or subtract durations, convert between time units, and find elapsed time — with step-by-step solutions.

Calculate

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

Can cross midnight (23:00 → 06:00)

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

Complete User Guide

What Is Time Duration?

Time duration is the amount of time that passes between two points, or the length of a time interval. This calculator finds duration between clock times, adds or subtracts duration from a time, converts between 7 time units (seconds to years), and computes end time from a start time and elapsed duration — with automatic midnight-crossing support.

4 Calculation Types

Duration Between Times

Enter start and end time. Duration can cross midnight. Shows result in seconds, minutes, hours, and days.

Add / Subtract

Add or subtract hours, minutes, seconds, or days from any clock time.

Convert Units

Convert between seconds, minutes, hours, days, weeks, months, and years.

Elapsed Time

From a start time and elapsed duration, find when it ends. Shows days elapsed.

Key Formulas

Duration: End − Start (or 86400 − Start + End)

Add: Time + Duration → mod 86400

Convert: Value × FromFactor ÷ ToFactor

Elapsed: Start + Duration = End

Important Notes

  • Use 24-hour format: 0:00 to 23:59. Midnight crossing is handled automatically.
  • Months and years are approximate: 1 month = 30 days, 1 year = 365 days.
  • Elapsed time shows how many days later the end time falls.

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