SwiftShort answer
Elapsed time = end minus start, borrowing 60 minutes when needed, and adding 24 hours when the end time is earlier because the span crosses midnight. 22:45 to 02:20 is 3 h 35 min, not a negative number. Totals add hours and minutes separately with a 60-minute carry, and decimal conversion divides minutes by 60.
Scope and assumptions
Durations are wall-clock arithmetic; DST transition days make some days 23 or 25 hours long. For billing or payroll, follow the governing policy. This page is informational.
The night-shift version of this question is the one that actually matters: a shift from 22:45 to 02:20 is 3 hours 35 minutes, not a negative number. End minus start, borrowing 60 minutes when needed — and when the end time is smaller than the start, the span crosses midnight, so add 24 hours to the end before subtracting.
Find your scenario
- Weekly totals and overtime? → Hours guide
- Days, not hours? → Days Between Dates guide
- Countdown to an event? → Birthday Countdown guide
What is a time duration calculator?
A time duration calculator measures elapsed time between two clock times, including spans that cross midnight, and totals mixed durations. Decimal conversion turns the result into a number payroll and billing can use.
Elapsed time crossing midnight: the two mechanics
Borrowing. 8:15 AM → 12:40 PM: minutes 40 − 15 = 25, hours 12 − 8 = 4 → 4 h 25 min. When end minutes are smaller — 9:50 → 11:20 — borrow: 20 + 60 − 50 = 30 minutes, hours 11 − 9 − 1 = 1 → 1 h 30 min.
The midnight borrow. 22:45 → 02:20: 02:20 + 24 h = 26:20; 26:20 − 22:45 = 3 h 35 min. Any calculator returning a negative duration has skipped this step.
Worked example: one night shift and one day block
| Span | Start | End | Duration |
|---|---|---|---|
| Overnight event | 22:45 | 02:20 (+1 day) | 3 h 35 min |
| Morning shift | 8:15 | 12:40 | 4 h 25 min |
| Total | 8 h 00 min |
Add 3d 7h 45m and 12h 30m: totaling mixed durations
Add hours and minutes separately, then carry every 60 minutes:
| Segment | Value |
|---|---|
| Build phase | 3 d 7 h 45 m |
| QA phase | 12 h 30 m |
| Launch prep | 1 d 22 h 05 m |
45 + 30 + 05 = 80 m = 1 h 20 m 7 + 12 + 22 + 1 = 42 h = 1 d 18 h Total: 5 d 18 h 20 m
Convert 95 minutes to hours and minutes: decimal hours for billing
Divide minutes by 60; never treat the decimal as minutes:
| h:mm | Decimal |
|---|---|
| 7 h 35 m | 7.58 |
| 95 min | 1.58 |
| 45 min | 0.75 |
1.58 hours is 1 h 35 min, not 1 h 58 min — the single most common timesheet error, and the one clients notice.
23 and 25 hour days: the DST timesheet trap
Twice a year the wall clock lies. On November 1, 2026 (US fall-back), a night shift from 22:00 to 06:00 covers nine hours on the clock but ten hours of actual work — the 1:00–2:00 AM hour happens twice. On March 14, 2027 (spring-forward), the same shift label covers only eight hours of work, because 2:00–3:00 AM never occurs.
Payroll counts hours actually worked, not the span printed on the schedule. Any duration calculation that spans a DST transition needs the local rules checked, or it will be off by exactly one hour — the kind of error that never shows up in testing and always shows up on a timesheet audit.
The same caution applies to travel planning in miniature: a flight scheduled to arrive at 01:30 local time on a fall-back night may have an arrival window that repeats an hour of clock time, and a spring-forward crossing can compress the schedule. Airlines publish block times in local time at each end for exactly this reason; when precision matters, convert both ends to UTC first and subtract.
Cross-midnight spans need one borrow: use the Time Duration Calculator and hours-between tool to total any pair of times. The longer version: how many hours a year a 15-minute standup is.
Midnight is a wall-clock problem, not an arithmetic problem
- Subtracting past midnight without adding 24 hours to the end time.
- Writing 12:00 AM for noon — midnight is 12:00 AM, noon is 12:00 PM.
- Mixing decimal and h:mm in one total.
FAQ
Q: How many hours between 22:45 and 02:20? 3 h 35 min — add 24 hours to the end time because the span crosses midnight.
Q: How do I calculate elapsed time? Subtract start from end, borrowing 60 minutes when the end minutes are smaller.
Q: What is 8:15 AM to 12:40 PM? 4 h 25 min.
Q: How do I add mixed durations? Add hours and minutes separately, then carry every 60 minutes into an hour: 3 d 7 h 45 m + 12 h 30 m + 1 d 22 h 05 m = 5 d 18 h 20 m.
Q: How do I convert 7 h 35 min to decimal? 35 ÷ 60 = 0.5833, so 7.58 decimal hours.
Q: Why is my duration negative? The end time is earlier because it crosses midnight — add 24 hours to the end time before subtracting.
Q: Do DST changes affect duration? Wall-clock spans on transition days can be 23 or 25 hours; elapsed-time math assumes a normal day.
Q: Is 12:00 AM midnight or noon? 12:00 AM is midnight and 12:00 PM is noon — the classic ambiguity, and the reason 24-hour notation exists.
Sources: 24-hour clock conventions (en.wikipedia.org/wiki/24-hour_clock); decimal time conventions (en.wikipedia.org/wiki/Decimal_time).
Disclaimer: Durations are wall-clock arithmetic; DST transition days make some days 23 or 25 hours long. For billing or payroll, follow the governing policy. This page is informational.