Time Calculator
Add or subtract up to 100 durations. Use signed clock durations or decimal hours, minutes or seconds, then compare the exact total and running sums.
YOUR CALCULATION
Result
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Calculation steps
Work through one step at a time or reveal the complete calculation. The steps use your current inputs.
How to calculate
Convert each signed duration to an integer number of milliseconds. Add the signed values in order, keep a running total and format the final result as hours, minutes and seconds. A negative total is allowed.
total duration = Σ signed durations; 1 hour = 60 minutes; 1 minute = 60 seconds; 1 day here = 24 hours
Worked example
1:30 + 2:45 − 0:15 means 1 hour 30 minutes plus 2 hours 45 minutes minus 15 minutes, giving 4:00:00, or 4 decimal hours.
Assumptions and input details
Clock h:mm means hours:minutes, not minutes:seconds. Seconds may have up to three decimal places; decimal-unit inputs also allow at most three places. One leading sign applies to the whole entry. Enter one duration per line; comma or semicolon separators also work, but blank entries and expressions are rejected. Up to 100 entries and 1,000,000 hours per entry are supported. Millisecond addition is exact within these limits; converted decimal units may be rounded for display. This adds durations, not times of day, dates, time zones or daylight-saving transitions. The graph shows the first 20 entries; the table includes every entry.
Using this calculator
Can I enter my own problem?
Yes. Replace the example values with your own inputs. The result, calculation steps, tables and applicable diagrams update from those inputs. Blank or invalid values clear the result; example values are never silently substituted for missing inputs.
Are the results exact?
Results use floating-point arithmetic and displayed rounding. Read the formula, assumptions and any stated data precision before interpreting the result.
Is my input uploaded?
The calculation runs in your browser. No account, file upload or external AI service is required. Inputs are not saved between page reloads.
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