Elapsed Time: How Long Did It Take?
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Elapsed time is how much time passes between a start and a finish. The easiest way: jump to the next o’clock first, then jump the rest, then add the jumps. From 3:45 to 4:20 is 15 + 20 = 35 minutes.
From “what time is it?” to “how long?”
Reading a clock answers when. Elapsed time answers how long. If Digi starts running at 3:00 and stops at 3:20, the time between the two is 20 minutes — the elapsed time. Children often find this shift harder than reading the clock itself, because there are now two times to think about at once.
The jump method
The trap is to subtract the clock numbers as if they were ordinary numbers: 420 − 345 = 75. That gives the wrong answer because an hour has 60 minutes, not 100. Instead, jump along a timeline:
- 3:45 → 4:00 is a jump of 15 minutes (to the next o’clock).
- 4:00 → 4:20 is a jump of 20 minutes.
- Add the jumps: 15 + 20 = 35 minutes.
For longer times, add whole hours in the middle: 2:30 to 4:15 is 30 minutes to 3:00, one hour to 4:00, and 15 minutes more — 1 hour and 45 minutes.
Seconds add up too
The same thinking works for seconds. Every full lap of a stopwatch is 60 seconds, which is one minute. So 120 seconds is 2 minutes, and 90 seconds is 1 minute and 30 seconds.
Try at home
- Time something real. Note the time when you start brushing teeth or a walk round the block, and again when you finish. How long did it take?
- Draw the jumps. Draw a line, mark the start and finish times, and draw a hop to the o’clock first. Write each hop above the line.
- Countdown questions. Dinner is at 6:00 and it’s 5:35 — how long do we have? Jump to the o’clock to find out.
Need a refresher? Read how to read a clock or quarter past and quarter to.