Time Calculations: Durations & Timetables

ME15Time Calculations

Durations, timetables and the number-line trick.

Work out how long things take by bridging through the o'clocks.

The film starts at 2:45 and ends at 4:20. How long is it?

2:45 → 3:00 → 4:00 → 4:20

15 min + 1 hour + 20 min

1 hour 35 minutes

Bridge through the next o'clock — never column-subtract times.

Learn the 3-Step Method

1Jump to the next o'clock.

2:45 → 3:00 is 15 minutes.

+15 min

2Jump whole hours.

3:00 → 4:00 is 1 hour.

+1 hour

3Jump the last minutes.

4:00 → 4:20 is 20 minutes. Total: 1 h 35 min.

+20 min

💡 Key IdeaTime is base 60 — column subtraction goes wrong (4:20 − 2:45 is NOT 1:75). Bridge instead.

Worked Example

A train leaves at 09:35 and arrives at 11:10. How long is the journey?

To 10:00

25 min

→

To 11:00

1 hour

→

To 11:10

10 min

→

✓ Total

25 + 60 + 10 = 95 min

1 h 35 min

Watch Out! Common Mistakes

Column-subtracting times.

4:20 − 2:45 = 1:75 ✕

Wrong! There’s no such time as 1:75 — an hour has only 60 minutes. Bridge through the o’clocks: 1 h 35 min.

Treating 1.5 hours as 1 h 50 min.

1.5 hours = 1 h 50 min ✕

Wrong! 0.5 of an hour is 30 minutes: 1.5 h = 1 h 30 min.

Misreading timetables.

Careful! Read DOWN a timetable column for one journey. The next column is a different train.

⬇ Cheat Sheet

TIME CALCULATIONS

Bridge: to the next o'clock → whole hours → final minutes.
Add the jumps.
Never column-subtract clock times.
1.5 hours = 1 h 30 min (not 1 h 50).

Example: 09:35 → 11:10 = 25 + 60 + 10 = 1 h 35 min

📖 Continue Your Journey

✓ ME1 Units of Length ✓ ME2 Converting Length ✓ ME3 Units of Mass ✓ ME4 Converting Mass ✓ ME5 Units of Capacity ✓ ME6 Converting Capacity ✓ ME7 Reading Scales ✓ ME8 Perimeter ✓ ME9 Area of Rectangles ✓ ME10 Area of Triangles ✓ ME11 Area of Parallelograms ✓ ME12 Compound Shapes ✓ ME13 Volume of Cuboids ✓ ME14 Telling the Time ME15 Time Calculations ME16 Money Calculations ME17 Imperial and Metric Units ME18 Measurement Problem Solving

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Next Lesson: ME16 Money CalculationsPounds, pence and getting the right change.

📄 Free printable: Download the Time Calculations cheat sheet (PDF) — keep it by your child's desk.

Quick summary

Bridge through the o'clocks: next hour, whole hours, final minutes.
9:35 to 11:10 = 25 min + 1 h + 10 min = 1 h 35 min.
Never column-subtract times — hours have 60 minutes, not 100.
1.5 hours means 1 hour 30 minutes.

Frequently asked questions

How do you work out how long something lasts?

Bridge through the o'clocks: from the start time jump to the next whole hour, then whole hours, then the remaining minutes, and add the jumps.

Why can't you subtract times like normal numbers?

Because time is base 60 — column subtraction borrows tens, which invents impossible times like 1:75.

How should children read a bus or train timetable?

Each column is one service, read downwards. Find the departure and arrival in the same column, then bridge to find the journey time.

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