How to Calculate Time Duration: A Step-by-Step Guide

Updated 5 Oct 2026 in Date & Time

Calculates hours and minutes between two times, including overnight shifts.

Dates and durations matter for notice periods, leave planning, project deadlines and contracts. Counting days on a calendar is slow and easy to get wrong, especially across months of different lengths.

What you need

• Start time
• End time

Step by step

1. Enter the start time.
2. Enter the end time.
3. The results update as you type, or press Calculate.
4. Read the duration first, then the supporting figures below it.

The formula

Duration = end − start (+24 h if end is earlier).

Worked example

For example, with these inputs:

• Start time: 09:00
• End time: 18:30

the calculator returns:

• Duration: 9 h 30 min
• In hours: 9.50 hours

Practical tips

• Write dates in an unambiguous format such as 5 Oct 2026 when sharing deadlines.
• Months have different lengths, so 'one month' is not always 30 days.
• Convert times to minutes before subtracting, then convert back to hours and minutes.
• Public holidays are not weekends; subtract them separately when counting working days.

Background

Many Singapore rules are expressed in days: notice periods, leave entitlements, stamp duty deadlines and probation periods. Whether the count includes the start or end date, and whether weekends count, changes the answer.

When sharing dates internationally, write the month as a word to avoid confusion between day-month and month-day formats.

Singapore has 11 gazetted public holidays a year, and when one falls on a Sunday the following Monday is a holiday. Working-day calculations therefore need holidays removed separately from weekends.

Related calculations

• Age Calculator: Calculates exact age in years, months and days.
• Days Between Dates Calculator: Counts days between two dates.
• Add Days to a Date Calculator: Finds the date a number of days after another date.
• Subtract Days from a Date Calculator: Finds the date a number of days before another date.

Want to skip the arithmetic? The free Time Duration Calculator does all of this instantly and updates as you type.

Run your own numbers: Time Duration Calculator