date-time calculator
Time Calculator
Add or subtract hour, minute, and second durations with normalized results.
Time arithmetic
Add or subtract time
Result
Enter time values and choose Calculate.
Formula version 1.0.0 · Date and time-zone rules are excluded.
How to use this calculator
- Choose Add or Subtract.
- Enter both hour-minute-second values.
- Select Calculate.
- Review normalized time, decimal hours, and seconds.
Symbols and units
| Symbol | Meaning | Unit or domain |
|---|---|---|
h | Hours | Hours |
m | Minutes | Minutes |
s | Seconds | Seconds |
Checked examples
Add time
Inputs: 1:30:45 + 0:45:30
Calculation: 5445 + 2730 seconds
Result: 2:16:15
The sum is normalized through seconds.
Check: time-basics.test.ts — adds time
Subtract time
Inputs: 2:00:00 − 0:30:30
Calculation: 7200 − 1830 seconds
Result: 1:29:30
A signed result is allowed.
Check: time-basics.test.ts — subtracts time
Assumptions, rounding, and limits
- Every hour is 3,600 seconds.
- Inputs are durations, not clock dates.
- Negative subtraction results are shown with a sign.
- Displayed decimal hours derive from total seconds.
Frequently asked questions
Can minutes exceed 59?
Values normalize through total seconds, but standard 0–59 entries are easiest to review.
Does it handle dates?
No. Use Date Difference for calendar spans.
Why is the result normalized?
Every 60 seconds becomes a minute and every 60 minutes becomes an hour.
Sources and review
- BIPM: SI Brochure — Accepted units of time and SI second
- W3C: Date and Time Formats — 24-hour time notation
- Formula version
- time.calculator@1.0.0
- Formula review
- Equatara formula review
- Editorial review
- Equatara editorial review
- Last verified
- 2026-10-25
- Applicability
- Global clock arithmetic without dates, zones, payroll, or legal rules.
- Next review
- On material change or by 2028-10-25.
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Found a problem?
Report a formula, result, example, source, or accessibility issue through the calculator correction process. Do not include sensitive input values.