Date and time

Time Duration Calculator

Measure the hours and minutes between two clock times, with overnight shifts handled correctly.

FreeNo sign-inReviewed 4 November 2026

Awaiting input

Fill in the fields and press Calculate. Your result appears here and stays in view as you scroll.

The guide

Understanding the Time Duration

Measure the hours and minutes between two clock times, with overnight shifts handled correctly.

What each input means

The calculator asks for 3 pieces of information. Every field is validated before the maths runs, so an impossible value is refused rather than quietly producing a wrong answer.

Input	What it asks for	Example
Start time	A clock time.	Today
End time	A clock time.	Today
Unpaid break	A number in min, at least 0 and no more than 1440.	30 min

A worked example using the default inputs

With unpaid break of 30 min, the calculator returns 8h 0m 480 minutes.

Result line	Value
Duration after break	8h 0m 480 minutes
Decimal hours	8.00
Gross span	8h 30m
Break deducted	30 min
Crosses midnight?	No

The same arithmetic runs whatever you type into the form above, so you can reproduce any figure by matching the inputs listed here.

How this is calculated

Minutes = (end − start), adding 1440 if negative, then subtract the unpaid break. Decimal hours = minutes ÷ 60.

Working values are kept at full precision and rounded only for display. Impossible dates, zero denominators, negative amounts where they make no sense, and out-of-range values are rejected before any result is shown.

How dates and times are counted here

Date arithmetic is done on calendar dates, not on a count of milliseconds, so month lengths and leap days behave the way a wall calendar does. That single decision removes almost every off-by-one you see in spreadsheet date maths.

Question	The rule	Where it is used
How far apart two dates are	Count calendar days between them; state whether the end day is included	Date difference, age
Move a date forward or back	Step the day or month, then clamp to the target month length	Add or subtract days
How long a shift was	Finish − start − breaks, wrapping past midnight	Time duration, hours
What time is it elsewhere	Convert to UTC, then out through the IANA zone database	Time zone converter
How old someone is	Completed years, then months, then days	Age

The inclusion convention is the usual source of disagreement. "One week from Monday" is the following Monday, which is seven days later but eight dates if you count both Mondays. Every tool states which convention it used in the result, so two answers that differ by one can both be right.

Daylight saving is not a fixed offset. Zones in the database carry their historical rule changes, which is why a meeting booked across a DST boundary can shift by an hour even though both cities look unchanged.

Three worked examples from this section

1 March to 31 March

Excluding the start date gives 30 days, which is the usual "days between" answer. Counting both ends, as a hotel or a project calendar would, gives 31. Neither is wrong; the convention is the whole difference.

A shift from 14:00 to 22:30 with a 30-minute break

The clock difference is 8 hours 30 minutes. Taking off the unpaid break leaves 8 hours exactly, which is 8.0 in decimal hours for payroll.

Clock difference: 8 h 30 m
Less unpaid break: 8 h 0 m
Decimal hours for payroll: 8.00

09:00 in Sydney, seen from London

During daylight saving Sydney runs at UTC+11. Nine in the morning there is 22:00 UTC the previous day, and London in winter is UTC+0, so the same moment reads as 22:00 on the day before. In July, when Sydney is UTC+10 and London is UTC+1, the gap narrows to nine hours.

How days, months and time zones are counted

Date arithmetic is performed on calendar dates rather than on elapsed milliseconds, so month and year lengths are handled correctly and leap days are respected. Where a difference is reported, the convention used (whether the end date is included) is stated in the result.

Time zone conversions use the IANA time zone database, which carries each region's daylight saving rules and their historical changes.
Adding months to the 31st can land on a shorter month; the standard convention is to move to that month's last day.
Dates are interpreted in your device's local time zone unless the tool asks for a zone explicitly.