TetraKits
Adding 2 hours 45 minutes to 2:30 PM, or finding how long a meeting ran from 9:15 to 11:42, should not require mental arithmetic. The TetraKits time calculator handles clock-time add/subtract and duration math in your browser — free, instant, and private.
Pair it with the date calculator for calendar days and the world clock for international scheduling.
Overview
Time math converts hours, minutes, and seconds to a total second count, performs the operation, then converts back to HH:MM:SS. When adding time crosses midnight, results wrap at 24 hours. Duration mode finds elapsed time between two clock times, including overnight spans.
How to add and subtract time
- Open the Time Calculator and stay on Add / Subtract.
- Enter the start time in hours, minutes, and seconds.
- Enter the offset — use negative values to subtract (e.g. −1 hour, −30 minutes).
- Read the result time and breakdown in the results panel.
Example: Start 14:30:00 + offset 2:45:00 = 17:15:00.
Duration mode
Switch to Duration, enter a from-time and to-time. The calculator returns hours, minutes, and seconds elapsed. If the end time is earlier than the start (e.g. 22:00 to 06:00), it assumes the span crosses midnight.
Use cases
- Payroll and shifts: Calculate end-of-shift time from start time plus hours worked.
- Cooking: Add prep and cook durations to a start time.
- Travel: Find layover length between arrival and departure times.
- Project tracking: Measure elapsed time between two timestamps in a day.
Frequently asked questions
How do I add 2 hours 30 minutes to 9:00 AM?
Enter start 9:00:00 and offset 2:30:00. Result: 11:30:00.
Can I subtract time?
Yes. Use negative values in the offset fields.
What is the difference from the date calculator?
Time calculator = hours/minutes/seconds within a day. Date calculator = calendar days between dates.
Does it handle midnight?
Yes. Add mode wraps at 24 hours. Duration mode handles overnight spans.
Is this time calculator free?
Yes. Unlimited use, no signup, all local.
