Time Calculator
Add or subtract time durations, compute a future or past date and time, or evaluate a full time expression in one step.
Add or Subtract Two Time Values
Add or Subtract Time from a Date
Time Calculator — Expression Form
d (days), h (hours), m (minutes), s (seconds)
and the operators + and −.Example:
1d 2h 3m 4s + 4h 5s - 2030s + 28h
How the Time Calculator Works
All three calculators normalize time automatically. Entering 90 minutes produces 1 hour, 30 minutes — hours and days are carried over so the result is always in the most readable form. Large values like 100,000 seconds are expressed as whole days, hours, minutes, and seconds.
The date calculator converts your start date and time to a precise timestamp, applies the duration in seconds, then converts the result back to a calendar date and clock time — handling leap years, daylight-saving transitions, and month boundaries correctly. For a dedicated date interval finder, try the date calculator.
The expression form reads left-to-right, accumulating totals as it encounters each value-unit pair. The sign of an operator (+ or −) applies to every subsequent value until the next operator.
Common Use Cases
- Shift Duration: Add the hours of multiple shifts across a week to find total hours worked. For the elapsed time between two specific clock times, try the time duration calculator.
- Video & Podcast Editing: Sum segment durations to check total runtime before exporting.
- Project Time Tracking: Subtract logged hours from allocated budget to see remaining capacity.
- Deadline Calculation: Add a fixed turnaround (e.g. 3 days, 4 hours) to a submission date to find the due time.
- Countdown Events: Subtract now from an event time to get the exact hours, minutes, and seconds remaining. For a day-by-day countdown, try the day counter.
Worked Example
Add 3 h 45 min to 14:30 → 18:15. Expression form: 3h 30m + 45m − 15m = 4 h 00 min. Date calculator: Monday 09:00 + 2 days 8 hours 30 minutes = Wednesday 17:30. For shift totals: 8h 15m + 7h 45m + 9h = 25 h 00 min (1 day 1 hour) — the result auto-normalises to days when totals exceed 24 hours.
Frequently Asked Questions
How do I add or subtract time?
Use the Time/Date Calculator tab. Select Add or Subtract, enter a starting time or date, then enter the hours, minutes, and seconds to add or subtract. For complex multi-unit expressions, use the Expression tab — for example, 3h 30m + 45m - 15m computes to 4 hours.
How do I calculate the time between two dates?
Use the Date Calculator tab. Enter your start and end dates and times, and the calculator returns the exact duration in days, hours, minutes, and seconds. It correctly handles leap years, month boundaries, and daylight saving time transitions.
How does the expression input work?
Type natural time expressions like 2h 30m + 45m or 1d 3h - 2h 15m. The expression parser handles hours (h), minutes (m), seconds (s), and days (d). Addition and subtraction can be chained in a single expression.
Does the calculator handle daylight saving time?
Yes. When calculating the duration between two specific dates and times, the calculator correctly accounts for DST transitions so the result reflects clock time, not just elapsed seconds. Arithmetic operations (add/subtract) work in fixed units regardless of DST.
Related calculations
For the gap between two times rather than adding to one, use the time duration calculator. Across dates rather than within a day, the date calculator counts whole days and the business days calculator counts only working ones.
Privacy & Data
Everything runs in your browser. No inputs are sent to a server; all computation is done locally with JavaScript. Your times, dates, and expressions are never stored or shared.
Evidence & Methodology
How This Page Is Grounded
Method
Converts hours, minutes and seconds to a common duration, adds or subtracts, then normalises the result.
Important limitation: This is duration arithmetic and does not model civil-time changes such as daylight-saving transitions.
Primary Sources
- ISO 8601 date and time format International Organization for Standardization
Quality Checks
Carry, borrow, negative duration and 24-hour rollover cases are checked.
See how sources are selected and corrections are handled in our Editorial & Calculation Methodology, and which automated checks this page has to pass in How We Test.