What Is the Time Calculator?
The Time Calculator is a free tool with two powerful modes. Time Between mode calculates the exact duration between any two date-and-time points — down to seconds. This is ideal for calculating work hours, project durations, how long an event lasted, or the time until a deadline. Add / Subtract Time mode lets you add or subtract a duration to a start time, giving you the exact resulting time — useful for scheduling and planning.
Time calculations are surprisingly tricky to do mentally because of the non-decimal nature of minutes and seconds (base 60) and because days have 24 hours rather than 100. This calculator handles all of that automatically and instantly.
How to Use the Time Calculator
- Choose your Mode: "Time Between" to find duration, or "Add / Subtract" to shift a time.
- Time Between: Enter a start date and time and an end date and time, then click Calculate Duration.
- Add / Subtract: Enter a start time, choose Add or Subtract, enter hours/minutes/seconds, then click Calculate.
- Results appear instantly in the results panel below the button.
Time Calculation Formula
Common Time Durations Reference
| Duration | Hours | Minutes | Seconds |
|---|---|---|---|
| 1 minute | 0.0167 hrs | 1 min | 60 sec |
| 1 hour | 1 hr | 60 min | 3,600 sec |
| 8-hour workday | 8 hrs | 480 min | 28,800 sec |
| 1 day | 24 hrs | 1,440 min | 86,400 sec |
| 1 week | 168 hrs | 10,080 min | 604,800 sec |
| 30 days | 720 hrs | 43,200 min | 2,592,000 sec |
When to Use This Calculator
The time calculator is useful whenever you need to measure or manipulate time with precision. Common use cases include: calculating billable work hours between clock-in and clock-out times, determining how long a project or meeting lasted, finding out what time a flight or drive will arrive given a departure time and duration, calculating overtime hours, and planning events that need to start or end at a specific time.
It also handles cross-midnight calculations automatically. If you worked from 10:00 PM to 6:00 AM, simply enter both times and the calculator will give the correct 8-hour result. For time spans spanning multiple days, use the datetime-local inputs in Mode 1 which include the date component.