Formula
duration = end seconds − start seconds (+ 86,400 if next day)
Convert both clocks to seconds since midnight, add 86,400 seconds to an overnight end, then subtract.
Date & time
● Runs locallyTime Duration
Find the elapsed duration between two clock readings without attaching them to a time zone. Mark an overnight end explicitly so an earlier clock time is never guessed as the next day.
Example values
Elapsed time
Assumptions
- No daylight-saving or time-zone transition is applied.
- Next-day mode adds exactly one 24-hour day.
This calculator handles clock intervals under 48 hours. Use date difference for multi-date spans.
Formula review
Formula v1.0.0
Reviewed 2026-08-03
CalcFlow engineering review
Time Duration: Worked example
22:45 is 81,900 seconds. 01:15 next day is 90,900 seconds on the same timeline, leaving 9,000 seconds or 2 h 30 min.
Frequently asked questions
Why must I mark the next day?
An end earlier than the start is ambiguous. The explicit control prevents the calculator from guessing.
Are daylight-saving changes included?
No. This is clock arithmetic. Use a time-zone-aware scheduling tool for real instants across transitions.
Can the interval exceed 24 hours?
Next-day mode supports up to a 48-hour clock interval in V1.