This time calculator handles duration math in several different modes: building a total from multiple add/subtract time entries, comparing two times for their percentage difference, evaluating a free-form time expression, and multiplying or dividing a time value.
How to use this time calculator
- Choose a tab: Duration, Date & Time, Expression, or Multiply/Divide.
- In Duration mode, pick Add/Subtract Rows to build a running total, or Compare/% Difference to compare two time values.
- Enter days, hours, minutes, seconds, and milliseconds as needed for your chosen mode.
- The result updates live, including a decimal-hours view for the primary result.
Add/Subtract Rows vs. Compare/% Difference
Add/Subtract: Total = Row 1 ± Row 2 ± Row 3 … | Compare: % Difference = |A − B| ÷ ((A+B)/2) × 100
Add/Subtract Rows mode builds up a cumulative total from any number of time entries, each with its own plus or minus operator — useful for tallying billable hours or combining multiple durations. Compare/% Difference mode instead takes exactly two time values and reports their ratio and percentage difference, which answers a different question: not “what’s the total,” but “how far apart are these two durations.”
When to use Expression or Multiply/Divide instead
The Expression tab lets you type a free-form time calculation directly rather than filling in separate rows. The Multiply/Divide tab handles a different kind of problem — scaling a single time value up or down by a factor, such as finding half of a duration or tripling a time estimate, which isn’t the same operation as adding or comparing two separate times.
Frequently asked questions
What’s the difference between the Duration tab and the Date & Time tab?
The Duration tab works with pure time spans (hours, minutes, seconds) independent of any calendar date. The Date & Time tab instead works with actual calendar dates and clock times, for questions like finding the time between two specific dates.
Can I subtract time entries, not just add them?
Yes — in Add/Subtract Rows mode, each row after the first has its own +/− operator, so you can subtract as well as add individual time entries when building your total.
Does this calculator save my previous calculations?
Yes — the History tab keeps a record of past calculations so you can refer back to them without redoing the entry.
