Time Adder Subtractor

The Time Adder Subtractor takes a start time of day and adds or subtracts a span of hours, minutes and seconds, telling you the resulting clock time and whether it rolled into the next day or back into the previous one.

It answers the everyday questions a calendar app glosses over: what time will a 4-hour-30-minute process finish if it begins at 22:15, when should you set off if a meeting is 90 minutes earlier, or what time it is after subtracting a flight duration.

Enter your start time as HH:MM or HH:MM:SS in 24-hour form, choose whether to add or subtract, then type the hours, minutes and seconds to shift by.

The tool sums the offset, applies it, and wraps the answer cleanly within a 24-hour clock while reporting the day shift, so 23:00 plus three hours correctly becomes 02:00 the next day.

Large offsets spanning several days are handled too, and a zero offset simply echoes the start time.

All of the arithmetic runs locally in your browser with no time zones or network involved, so results are deterministic and private; nothing you type is uploaded, logged or stored, and the tool keeps working offline once loaded.