How the duration is calculated
The calculator converts both date-times into an exact moment, subtracts them, and breaks the difference into days, hours and minutes. It also shows the same span as total hours, total minutes, days and weeks, so you can use whichever unit you need.
For example, from Monday 9:00 AM to Wednesday 3:30 PM is 2 days, 6 hours and 30 minutes — or 54.5 hours.
Daylight saving time
Durations are measured using your device’s time zone, so a span that crosses a daylight-saving change is measured in real elapsed time. A night shift from 10 PM to 6 AM on the night clocks “fall back” is actually 9 hours long; on the night they “spring forward” it is 7 hours. That matters for pay: under federal rules you are paid for the hours you actually work.
Adding and subtracting time
Use the second tool to answer questions like “what time will it be 90 minutes from now?” or “what date is 45 days before the deadline?”. Enter a starting date and time, choose add or subtract, and enter days, hours and minutes. Negative numbers also work.
Everyday examples
- How long a project, trip or rental lasted.
- Hours between two shifts (rest time between a closing and an opening shift).
- Counting down to an exam or event.
- Working out when a medication dose or a timer ends.
For shift times within a single day, the simpler hours calculator is faster.
Sources and limits
The rules on this page come from these official sources, which we read on September 26, 2026. Pay rules change and differ by state, and some employers and union contracts pay more than the law requires. This page is general information, not legal or payroll advice. If you think you have been underpaid, contact the U.S. Department of Labor's Wage and Hour Division or your state labor department.