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Elapsed Time: How Much Time Has Passed?

In one line: Elapsed time is how much time passes between a start time and an end time, and you find it by counting on from the start to the end.

Why it works

We use elapsed time every day: working out how long a film lasts, how long until dinner, or when to leave so you are not late. It also builds number skills, because time works in groups of 60 (60 minutes make 1 hour), not groups of 10 or 100 like ordinary numbers. Learning to count on in jumps helps children plan, solve real problems and check whether an answer makes sense.

Think of it like: Think of finding elapsed time like walking along a road with signposts at every 'o'clock' time (1:00, 2:00, 3:00 and so on). You start at your start time, take a short walk to the next signpost, then take big one-hour strides between signposts, then a short walk to your end time. Add up all the walks and strides, and that is how far you travelled in time. (Where this breaks: A real road keeps counting up forever, but a clock does not: the minutes go back to 00 after 59, and the hours go back to 1 after 12 (switching between a.m., before midday, and p.m., after midday). So you must watch for those reset points, which a normal road does not have.)

Worked example

A film starts at 2:45 p.m. and ends at 4:20 p.m. How long is the film?

  1. Start at 2:45 p.m. and jump to the next o'clock time, 3:00 p.m. That is 15 minutes.
  2. Jump in whole hours from 3:00 p.m. to 4:00 p.m. That is 1 hour.
  3. Jump from 4:00 p.m. to the end time, 4:20 p.m. That is 20 minutes.
  4. Add the jumps: 15 minutes + 1 hour + 20 minutes = 1 hour 35 minutes.
  5. Check: 2:45 plus 1 hour is 3:45, and 3:45 plus 35 minutes is 4:20. It matches.

Answer: The film lasts 1 hour 35 minutes.

Common mistakes

  • Subtracting times like ordinary numbers (420 − 245 = 175, so '1 hour 75 minutes') gives a wrong answer because an hour has 60 minutes, not 100; count on in jumps instead.
  • Forgetting that times change from a.m. to p.m. at midday (or p.m. to a.m. at midnight) leads to impossible answers; mark 12:00 as a signpost and jump across it carefully.
  • Writing more than 59 minutes in an answer, such as '2 hours 70 minutes', is incomplete; swap every 60 minutes for 1 extra hour (2 hours 70 minutes = 3 hours 10 minutes).
  • Counting the o'clock times you pass instead of the jumps between them adds an extra hour; count the gaps (3:00 to 4:00 is one jump, not two).

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Swimming practice starts at 3:00 p.m. and ends at 3:40 p.m. How long is practice?

Questions parents ask

What grade do kids learn elapsed time?

In the US, children usually start solving elapsed time problems in minutes in Grade 3, then tackle harder, multi-step problems in Grades 4 and 5. In the UK, durations are introduced around Year 3 and extended in Years 4 and 5, and in Australia similar work happens across Years 3 to 5.

How can I help my child with elapsed time at home?

Ask real questions during the day, such as 'Dinner is at 6:15 and it is 5:40 now, how long do we have?' Use an analogue clock or draw a simple number line with jumps to the next o'clock time, then whole hours, then the leftover minutes.

Why does my child find elapsed time so hard?

Time is grouped in 60s rather than 10s, so normal subtraction tricks do not work, and the change between a.m. and p.m. adds another step. Counting on in jumps with a number line usually makes it much clearer than trying to subtract the times.

Should my child use a number line or subtraction for elapsed time?

A number line (or 'counting on') is the most reliable method for most children in Grades 3 to 5 because it shows each jump and handles the 60-minute hour naturally. Older children can learn to subtract by exchanging 1 hour for 60 minutes, but only once they understand why that works.