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Time Duration Calculator

Q: How do I enter 12-hour times?

Convert to 24-hour clock first: 5:45 PM is 17:45, 12:30 AM is 00:30.

Q: What if the break is longer than the interval?

The calculator returns a CALCULATION_ERROR; check the times or the break length.

Computes the elapsed time between a start and an end clock time (24-hour HH:MM), optionally minus a break, handling intervals that cross midnight, and reports it as hours and minutes and as decimal hours.

When to use

You need the length of a shift, meeting, trip or any interval given two clock times on the same or consecutive days.

Do not use when: The interval spans more than 24 hours or several days (use date-difference), or you need weekly hours and pay (use work-hours).

Formula

gross_minutes = end − start (+ 1440 if end < start); total_minutes = gross_minutes − break_minutes; decimal_hours = total_minutes / 60

Identical start and end times give 0 minutes, not 24 hours. Daylight-saving transitions are ignored.

Inputs

Parameter	Type	Unit	Required	Description
`start_time`	string		yes	Start clock time in 24-hour HH:MM format.
`end_time`	string		yes	End clock time in 24-hour HH:MM format. An end time earlier than the start time is taken as the next day.
`break_minutes`	integer	min	default 0	Unpaid or excluded minutes to subtract from the interval. Range: ≥ 0, ≤ 1440

Outputs

Output	Type	Unit	Description
`total_minutes`	integer	min	Elapsed minutes after subtracting the break.
`hours`	integer	h	Whole hours of the duration.
`minutes`	integer	min	Minutes beyond the whole hours.
`decimal_hours`	number	h	total_minutes / 60, e.g. for timesheets.
`duration_text`	string		Duration as 'h h m min'.
`gross_minutes`	integer	min	Minutes from start_time to end_time before subtracting the break.
`crosses_midnight`	boolean		true when end_time is earlier than start_time and was taken as the next day.

Example

09:30 to 17:45 with a 30-minute break: {"start_time":"09:30","end_time":"17:45","break_minutes":30} → {"total_minutes":465,"hours":7,"minutes":45,"decimal_hours":7.75,"duration_text":"7 h 45 min","gross_minutes":495,"crosses_midnight":false}

Night shift 22:00 to 06:30: {"start_time":"22:00","end_time":"06:30"} → {"total_minutes":510,"hours":8,"minutes":30,"decimal_hours":8.5,"duration_text":"8 h 30 min","crosses_midnight":true}

GET https://tttkmbb.com/api/v1/calculate/time-duration?start_time=09%3A30&end_time=17%3A45&break_minutes=30

Machine access

API: GET https://tttkmbb.com/api/v1/calculate/time-duration (query parameters) or POST with a JSON body {"inputs": {...}}
Schema: https://tttkmbb.com/api/v1/calculators/time-duration · Markdown: https://tttkmbb.com/everyday/time-duration.md · JSON definition: https://tttkmbb.com/everyday/time-duration.json
MCP: server https://tttkmbb.com/mcp, tool run_calculator with calculator_id="time-duration"
OpenAPI operationId: calculate_time_duration
Freshness: static. Authentication: none. Rate limit: fair use (see rate limits).

Sources

ISO 8601 – Date and time format (Wikipedia) (reference)

FAQ

How do I enter 12-hour times?

Convert to 24-hour clock first: 5:45 PM is 17:45, 12:30 AM is 00:30.

What if the break is longer than the interval?

The calculator returns a CALCULATION_ERROR; check the times or the break length.

Related calculators

Work Hours Calculator — Weekly and monthly hours and pay from the same shift times.
Date Difference Calculator — Intervals spanning several days.