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date-time calculator

Time Duration Calculator

Find elapsed clock time for same-day or overnight start and end times.

Time arithmetic

Find elapsed clock time

Result

Enter time values and choose Calculate.

Formula version 1.0.0 · Date and time-zone rules are excluded.

How to use this calculator

  1. Enter Start time.
  2. Enter End time.
  3. Select next-day rollover when the end is after midnight.
  4. Calculate and review duration.

Symbols and units

SymbolMeaningUnit or domain
startStarting clock timeHH:MM[:SS]
endEnding clock timeHH:MM[:SS]
ΔtEnd minus startSeconds or normalized time

Checked examples

Same-day duration

Inputs: 09:15 to 17:45

Calculation: 63900 − 33300 seconds

Result: 8:30:00

The elapsed clock time is 8.5 hours.

Check: time-basics.test.ts — same-day duration

Overnight duration

Inputs: 22:30 to 01:15, next day

Calculation: Add 86,400 seconds before subtracting

Result: 2:45:00

The explicit rollover crosses midnight.

Check: time-basics.test.ts — overnight duration

Assumptions, rounding, and limits

  • No date or time zone is inferred.
  • Overnight rollover is applied only when selected.
  • Daylight-saving clock changes are excluded.
  • The maximum modeled rollover is one day.

Frequently asked questions

How do I cross midnight?

Select that the end time is on the next day.

Does daylight saving affect it?

No; this is clock arithmetic without zones or dates.

Are endpoints inclusive?

Duration is the end instant minus the start instant.

Sources and review

Formula version
time.duration@1.0.0
Formula review
Equatara formula review
Editorial review
Equatara editorial review
Last verified
2026-10-25
Applicability
Global clock arithmetic without dates, zones, payroll, or legal rules.
Next review
On material change or by 2028-10-25.

Found a problem?

Report a formula, result, example, source, or accessibility issue through the calculator correction process. Do not include sensitive input values.