TetraKitsTime Calculator
Stop doing time math in your head. Add or subtract hours, minutes, and seconds from any start time, or switch to Duration mode to find exactly how long passed between two clock times — including wraparound past midnight.
Read: Time Calculator Guide: Add, Subtract & Duration Online →
- Free to Use
- No Signup
- Privacy Friendly
How to use the time calculator
- 1
Add or subtract time
Select Add / Subtract, enter a start time (H:M:S), then enter the offset. Use negative hours to subtract (e.g. −1 hour).
- 2
Find duration
Switch to Duration, enter a from-time and to-time. The result shows hours, minutes, and seconds elapsed.
- 3
Pair with date tools
For calendar days, use the date calculator. For international meetings, check the world clock.
Time calculation formulas
Add/subtract: Convert start time to total seconds, add or subtract the offset, then convert back to HH:MM:SS (wrapping past midnight).
- 1 hour = 3,600 seconds
- 1 minute = 60 seconds
- Results wrap at 24 hours for time-of-day mode
Example: 14:30 + 2h 45m = 17:15.
Why Use This Tool?
Two Modes
Add or subtract time offsets, or find duration between two clock times.
Precise Input
Enter hours, minutes, and seconds separately for clarity.
Shift Planning
Perfect for work hours, travel layovers, and cooking timers.
Browser-Based
All math runs locally — no server calls.
Frequently Asked Questions
How do I add 2 hours 30 minutes to 9:00 AM?
Enter start time 9:00:00, offset 2:30:00. Result: 11:30:00. Results wrap at 24 hours if the sum crosses midnight.
Can I subtract time from a clock time?
Yes. Enter negative values in the offset fields (e.g. −1 hour, −15 minutes) to subtract from the start time.
How is duration between two times calculated?
Both times convert to seconds since midnight. Duration mode returns the shorter elapsed span, crossing midnight when the end time is earlier than the start.
What is the difference between this and the date calculator?
The time calculator works with hours, minutes, and seconds within a day. The date calculator adds calendar days or finds spans between dates.
Is my data saved?
No. All calculations run locally in your browser.
Exact Time Math for Work and Life
Shift workers tracking hours, cooks timing recipes, travelers calculating layovers, and freelancers logging billable time all need precise HH:MM:SS answers. This calculator replaces error-prone mental math with instant add, subtract, and duration results.
