Total hours:
Table of Contents
How the hour count is calculated
The calculator converts both dates to Unix timestamps (seconds elapsed since 00:00:00 UTC on 1 January 1970), subtracts the start from the finish, and divides by the number of seconds in an hour:
Hours = (Tfinish − Tstart) ÷ 3,600
- Tstart — Unix timestamp of the start date/time.
- Tfinish — Unix timestamp of the finish date/time.
- 3,600 — seconds in an hour (60 × 60).
Because Unix timestamps are UTC-based, the result is correct across daylight saving time transitions: a calendar day containing "spring forward" is 23 hours and "fall back" is 25 hours, and the calculator reflects this automatically.
Worked example using the calculator's default values (start = one month ago at 00:00, finish = today at 00:00):
- Start: 2026-06-08 00:00 one month ago → Tstart = 1778198400
- Finish: 2026-06-08 00:00 → Tfinish = 1780876800
- Difference in seconds: 2678400
- Hours = difference ÷ 3,600 = 744 hours
That's the value returned in the "Total hours" box above for the default range. The exact figure for a given month-long range varies between 672 (28-day February) and 744 (31-day month), with a 1-hour adjustment if a DST transition falls in the range.
Hours in common periods
For quick reference and cross-checking the calculator's output:
| Period | Hours | Derivation |
|---|---|---|
| 1 day | 24 | Definition (23 or 25 on DST transition days) |
| 1 week | 168 | 24 × 7 |
| 1 average month | ~730 | 8,760 ÷ 12 |
| February (non-leap) | 672 | 24 × 28 |
| 30-day month | 720 | 24 × 30 |
| 31-day month | 744 | 24 × 31 |
| 1 year (standard) | 8,760 | 24 × 365 |
| 1 year (leap) | 8,784 | 24 × 366 |
| 1 US full-time work year | 2,080 | 40 × 52 |
| 1 quarter (3 months) | ~2,190 | 8,760 ÷ 4 |
Elapsed hours vs work hours vs billable hours
These three counts answer different questions. Use the right one or you'll budget incorrectly.
- Elapsed hours (what this calculator returns). Total clock time between two timestamps, including nights, weekends, and holidays. Useful for SLA windows ("respond within 48 hours"), incubation times, and any wall-clock duration.
- Work hours. Hours within scheduled working time only — typically 8 hours a day, Monday to Friday, minus holidays. A 7-day elapsed week is 168 hours but only 40 work hours. Calculate by multiplying daily work hours by the count from the days calculator with the week-days option enabled.
- Billable hours. The subset of work hours actually spent on client/project tasks. Industry studies put utilisation at 60–80% of work hours for most knowledge workers, so a 40-hour work week usually yields 24–32 billable hours.
Payroll and shift calculations
For a single shift crossing midnight, treat the start as the previous day's date/time and the finish as the next morning's date/time — the calculator handles the day boundary correctly via the timestamp difference. For multi-day timesheets, summing individual shifts is more accurate than computing a single elapsed range because it excludes off-shift hours.
Common payroll periods, and their typical hour budgets at 40 hours/week:
| Pay period | Calendar days | Typical work hours |
|---|---|---|
| Weekly | 7 | 40 |
| Bi-weekly | 14 | 80 |
| Semi-monthly | 15–16 | 86.67 (avg) |
| Monthly | 28–31 | 173.33 (avg) |
Limitations and edge cases
- Time of day defaults to 00:00. The date pickers above accept dates only, so both start and finish are interpreted at midnight local time. For sub-day precision (e.g., 09:00 to 17:30), the displayed total will be in whole-hour chunks unless you adjust the input format.
- DST transitions. Spring forward removes 1 hour, fall back adds 1 hour. The calculator reflects this correctly via UTC-based timestamps. A range covering both transitions in a calendar year nets out to zero.
- Leap seconds. Civil time occasionally inserts a leap second (most recently in 2016), but Unix timestamps don't account for these. The error is at most 1 second over many years — safely ignorable for any practical purpose.
- Time zones. Both inputs are interpreted in your local time zone. If you copy times from a different zone without converting, the result will be off by the time zone offset (e.g., 5 hours for US Eastern to UTC).
- Negative ranges. If finish is before start, the result is negative. Always enter the earlier date first.
Sources & references
- ISO 8601 — the international standard for date and time representation. The YYYY-MM-DD format used in the inputs follows this standard.
- NIST Time and Frequency Division — US authoritative source for civil time. Operates the time.gov reference clock used by Windows, macOS, and most network time servers.
- IANA Time Zone Database — canonical source for time zone offsets and historical DST transition rules used by all major operating systems and programming languages.
- US Bureau of Labor Statistics — American Time Use Survey — reference for typical US work hours per week and per year.
FAQs
Enter your start and finish dates using the date pickers, then click Calculate. The calculator converts both inputs to Unix timestamps, subtracts the start from the finish, and divides by 3,600 — the number of seconds in an hour. The result is elapsed hours including nights and weekends.
There are 24 hours in a day, 168 hours in a week (24 × 7), about 730 hours in an average month (8,760 ÷ 12), and 8,760 hours in a standard 365-day year. A leap year contains 8,784 hours. A US full-time work year of 40 hours per week across 52 weeks is 2,080 hours.
Enter the start of the pay period as the start date and the end of the pay period as the finish date. The calculator returns total elapsed hours across that range, which includes nights and weekends. To get actual hours worked, multiply scheduled hours per day by the number of working days — or sum each individual shift.
Yes. The calculator works on any date range, from hours apart to years apart. Enter the earliest date as the start and the latest as the finish to get total elapsed hours. Note this is the full clock time elapsed, not work hours — a 7-day range returns 168 hours, not 40.
Divide hours by 24 to get days, or by 168 to get weeks. So 72 hours ÷ 24 = 3 days, and 336 hours ÷ 168 = 2 weeks. To convert hours to months, divide by approximately 730. The calculator returns hours directly — apply the conversion you need.
Yes, because it uses Unix timestamps which are absolute (UTC-based). A US calendar day containing the "spring forward" DST transition is 23 hours long; the "fall back" day is 25 hours. The calculator reflects this correctly — ranges crossing a DST transition will differ by 1 hour from the equivalent range outside DST.