Base-60 normalization
Values such as 90 minutes or 75 seconds are valid. They are converted to seconds first, so 90 minutes plus 75 seconds becomes 1h 31m 15s.
Exact time arithmetic
Time Calculator
Add or subtract durations in days, hours, minutes, and seconds, or shift a clock time forward or backward across midnight.
Your values stay in this browser page. A day in this calculator is exactly 24 hours; it does not apply calendar dates, time zones, or daylight-saving rules.
Duration tape
Enter two or more time values. Minutes and seconds may exceed 59; the result is normalized automatically.
Use the row operator to add or subtract. Negative totals are valid and keep one sign on the complete result.
Clock time +/- duration
Move one clock time forward or backward by an exact duration. The result includes the day offset when you cross midnight.
How the Time Calculator works
The calculator converts every entered duration to exact integer seconds, performs the requested addition or subtraction, then converts the signed result back to days, hours, minutes, and seconds.
1 minute = 60 seconds1 hour = 3,600 seconds1 duration day = 86,400 secondsSubtraction can go below zero
If the amount you subtract is larger than the base duration, the result is negative. The minus sign applies to the complete normalized duration instead of individual fields.
Clock rollover
Clock mode keeps a second-of-day plus an exact day offset. For example, 23:30:15 plus 2h 45m 50s becomes 02:16:05 on the next day.
Time calculation examples
Decimal hours are another representation
The exact result remains integer seconds. Decimal hours divide the signed total seconds by 3,600 and display up to six decimal places.
Different jobs stay separate
This app performs time arithmetic. It does not calculate elapsed work hours between start and end punches, weekly time cards, calendar-date differences, or time-zone conversions.
Private by design
Entered values stay in page memory. This version does not save calculations to browser work storage or send values to a Mycelgrid calculation API.
The fixed unit relationships used here follow NIST SP 330: a minute is 60 seconds and an hour is 60 minutes. The 24-hour day in this app is a duration unit, not a calendar or daylight-saving calculation.
Read how to add and subtract time Need weekly work punches? Open Time Card Calculator