How to use this calculator
- Enter your own values in the labeled fields. Check the units and assumptions before comparing results. Only the fields needed for your selected calculation mode are shown.
- Your answer updates automatically. Review the calculation steps to see exactly how it was calculated.
- Copy, share, save, or download your result. Saved inputs stay on this device.
How the calculation works
Durations are elapsed quantities, not local times or dates. Converting every entry to integer seconds preserves signs and supports totals above 24 hours. This calculation does not apply time zones, daylight-saving adjustments or payroll rounding. Review the units, period and assumptions before comparing scenarios. Displayed values are rounded, while the underlying calculation retains its available precision.
A worked example
12:30:00 + 15:45:30 − 01:15:00 = 27:00:30, or 97,230 seconds.
Reading your result
Use the main result together with its units and supporting figures. Display values are rounded; calculations keep their underlying precision. A change in inputs or assumptions can change the answer. Compare the step-by-step working with your intended use before relying on an estimate.
Frequently asked questions
What assumptions does this calculation use?
Durations are elapsed quantities, not local times or dates. Converting every entry to integer seconds preserves signs and supports totals above 24 hours. This calculation does not apply time zones, daylight-saving adjustments or payroll rounding.
Can I save or check a scenario?
The result includes the working and supporting values. Save and Restore keep inputs on this device; Copy, Download and Print export the result. Sharing a scenario explicitly includes the inputs in its link.
Sources & methodology
This calculator uses the mathematical identity and assumptions stated above. No current rates, prices, or external data are loaded. Conversion tools use international unit definitions.
Formula review: October 24, 2026. Read our methodology.