How to use this calculator
The business hours calculator measures time that falls inside a working schedule. Set the location, choose active weekdays, and enter up to two same-day opening intervals for each working day. Add closures for dates when the schedule does not apply. Then count working time between two local timestamps or add a duration of working time to a starting timestamp.
This is useful for support windows, service targets, and office availability. Time outside opening intervals does not count toward the result. The tool applies your schedule rather than assuming a universal nine-to-five day. Review lunch gaps, short weekdays, and closure dates before comparing the result with a service policy or another scheduling system.
Formula and calculation method
Working seconds = sum of the elapsed intersections between the requested time range and each open schedule interval.
Intersect the request with opening intervals
For each date, the tool checks its weekday and closure status. Eligible opening intervals are resolved in the selected time zone and clipped to the requested range. Only the overlapping elapsed seconds contribute to the result. A start before opening therefore counts from opening, and an end after closing counts only through closing.
Consume working time across dates
In addition mode, the requested duration is consumed only while the schedule is open. A target that cannot fit before closing carries its remaining working time to the next eligible interval. This differs from adding ordinary clock hours. The breakdown lets you review which dates supplied the time used to reach the target.
Worked examples
A target after the weekend
Use Monday–Friday, 09:00–17:00, without closures. Start on Friday, April 5, 2024 at 16:30 and add two working hours. Friday contributes 30 minutes. The remaining 90 minutes begin at 09:00 Monday, giving a target of Monday, April 8 at 10:30. The weekend contributes no working time.
Exclude a lunch interval
Configure 09:00–12:00 and 13:00–17:00 for a weekday. Count from 11:30 to 14:00 on that date. Thirty minutes before lunch and one hour after lunch qualify, giving 1h 30m. The 12:00–13:00 gap remains outside the schedule and requires no extra break deduction.
Move past a closure
Starting again at Friday 16:30, add two working hours but mark the following Monday closed. The 30 Friday minutes still count, while the remaining 90 minutes move to Tuesday morning. The new target is Tuesday 10:30. A closure skips the entire date rather than shortening its normal opening interval.
Edge cases and practical checks
Clock changes and interval shape
Working intervals are interpreted in a named time zone, so their elapsed length can reflect a clock transition. The schedule supports at most two same-day intervals per weekday and does not support an interval running overnight. Do not enter 22:00–06:00 as one interval; use a dated shift calculator for that kind of record.
Boundaries and search limits
A zero-width overlap contributes no time. A timestamp exactly at closing does not create another minute inside the schedule. Additions search within a five-year horizon, and an empty schedule cannot produce a positive target. If a result is unexpectedly far away, check disabled weekdays and closures before extending the intended planning range.
Frequently asked questions
How do I exclude lunch?
Create two opening intervals, such as 09:00–12:00 and 13:00–17:00. Time in the gap is outside working hours. Do not also subtract that lunch manually from the final answer; the interval model has already removed it from eligible time.
Does it count weekends?
Only weekdays enabled in your schedule count. You can enable weekend work or disable a weekday to match the actual operation. A configured closure then removes an individual date even if its weekday would normally be open. Review both settings together.
Are public holidays loaded automatically?
No. Enter the dates when the specific operation is closed. Observed holidays and one-off shutdowns vary between locations and organizations. A complete closure list is part of the input to this calculator, not a rule inferred from the selected time zone.
What if my start time is outside working hours?
The calculation waits until an eligible open interval before consuming working time. Starting after Friday closing can therefore push the first counted time into Monday, depending on the schedule and closures. Range mode similarly counts only the portion overlapping the open intervals.
Can I add negative working hours?
The business-hours addition mode takes a nonnegative duration. For a backward deadline question, establish a forward interval or use a schedule system that explicitly supports backward working-time search. Business-days subtraction is a separate whole-date operation and does not substitute for partial-day arithmetic.
Does this calculate a contractual service deadline?
It calculates the working-time assumptions you supply. Confirm the contract’s location, calendar, opening intervals, endpoint rules, and exceptions separately. A service policy can include pauses, priority-specific schedules, or other rules beyond the weekday-and-closure model supported here.
Published by TrueHour. Calculation methodology and sources · Report a correction · Time and date guides