How to Add and Subtract Time Values

Adding and subtracting time values follows the same carry and borrow rules as ordinary arithmetic, only with a base of 60 for seconds and minutes and a base of 24 for hours. When adding, work from seconds up to days, carrying 1 to the next unit whenever a total reaches 60 seconds, 60 minutes, or 24 hours.

When subtracting, work from seconds up to days as well, but borrow from the next highest unit whenever the bottom number is larger than the top number. For example, subtracting 56 minutes from 10 minutes requires borrowing 1 hour, turning it into 70 minutes before the subtraction can be completed.

How to Multiply and Divide Time Values

Multiplying and dividing time values both start by treating each unit, days, hours, minutes, and seconds, as a separate number before reconciling the totals into a clean result.

Multiplying Time by a Number

To multiply time by a number, multiply each of the four units separately, then convert any unit total of 60 or more, or 24 or more for hours, up into the next higher unit, carrying forward exactly as in addition.

Dividing Time by a Number or by Time

Dividing time by a number splits each unit by the divisor and then shifts any leftover decimal down into the next smaller unit, since a decimal day must become hours and a decimal hour must become minutes. Dividing time by time instead produces a plain ratio with no unit, showing how many times longer one duration is compared to the other.

Time Calculator Uses for Work and Daily Life

A time calculator has practical uses across work scheduling and daily life, from totaling hours across a work week to figuring out combined running or swimming split times. It also helps when subtracting lunch breaks from a shift, adding overtime onto a regular workday, or working out how long a series of timed tasks will take when added together.