Finding Elapsed Time

The big idea

Elapsed time is the amount of time between a start and an end. It helps to picture a clock or number line and move forward in manageable jumps. Hours contain 60 minutes, so crossing an hour is easier when a child first jumps to the next hour and then continues.

The jumps are parts of one duration. Add the jump lengths, not the clock readings.

Worked example

How much time passes from 2:45 to 4:10?

Jump from 2:45 to 3:00: 15 minutes. Jump from 3:00 to 4:00: 60 minutes. Jump from 4:00 to 4:10: 10 minutes. The total is 15 + 60 + 10 = 85 minutes, or 1 hour 25 minutes.

How children may show it

A child may draw an open number line labeled with the start, helpful hour marks, and the end. Another method is a table with “time reached” and “minutes added.” Both make the direction of time visible and reduce errors around the 60-minute boundary.

Common mix-up

Subtracting the displayed digits can produce an answer such as 4:10 − 2:45 = 2:35, which treats clock notation like an ordinary decimal. Ask whether 10 minutes can be reduced by 45 minutes without first regrouping one hour as 60 minutes.

Try it together

Choose two times during the day. Start at the earlier one and name the easiest next landmark: the next quarter hour, half hour, or whole hour. Record each jump and add the minutes. Then check that moving forward by the total reaches the ending time.