Time Durations and Timetables

Time is not base ten

Most numbers we work with are base ten — ten ones make a ten, ten tens make a hundred. But time is different. 60 minutes make 1 hour. That single fact is why so many people get time questions wrong.

If you try to subtract 14:50 from 15:20 by lining up the digits like ordinary numbers, you get into trouble, because you would borrow 100, when an hour is really only 60 minutes. The reliable method is to stop subtracting and start counting on.

This builds on reading the clock in The 24-Hour Clock, which timetables almost always use.

Counting on to find a duration

To find how long it is between two times, count on in three easy stages:

1. Up to the next whole hour — count the minutes.
2. Whole hours — count them in ones.
3. The last few minutes — count up to the final time.

Then add the three parts together.

Worked example 1: minutes only

How long from 09:20 to 09:55?

There is no whole hour to cross here, so it is one step:

1. From 09:20 to 09:55 is 35 minutes.

Done. When both times are in the same hour, just subtract the minutes.

Worked example 2: crossing the hour

How long from 10:40 to 12:15?

1. From 10:40 up to the next hour, 11:00 → 20 minutes.
2. From 11:00 to 12:00 → 1 hour.
3. From 12:00 to 12:15 → 15 minutes.

Add them: 1 hour + 20 min + 15 min = 1 hour 35 minutes.

Notice we never had to "borrow" anything — counting on did the hard part for us.

Worked example 3: adding a duration to a time

A train leaves at 16:50 and the journey takes 1 hour 40 minutes. When does it arrive?

1. Add the hours first: 16:50 + 1 hour = 17:50.
2. Add the minutes: 17:50 + 40 min. From 17:50 to 18:00 is 10 min, leaving 30 min, so → 18:30.

The train arrives at 18:30.

Reading a timetable

A timetable is a grid of times. The rule is simple:

• Each column is one bus or train. Read down a column to follow that one vehicle through every stop.
• Each row is one stop. Read across a row to see all the times that buses leave that stop.

Here is a small bus timetable:

Stop	Bus A	Bus B	Bus C
High Street	08:15	08:45	09:20
Market Square	08:27	08:57	09:32
Hospital	08:41	09:11	09:46
Station	08:55	09:25	10:00

To find when Bus B reaches the Hospital, go down the Bus B column to the Hospital row: 09:11.

Worked example 4: a timetable journey

You catch Bus A at the High Street and ride to the Station. How long is the trip?

1. Departs High Street: 08:15.
2. Arrives Station: 08:55.
3. Count on: from 08:15 to 08:55 is 40 minutes.

The journey takes 40 minutes. If you wanted to be at the Station by 09:30, both Bus A (08:55) and Bus B (09:25) would get you there in time, but Bus C (10:00) would be too late.

Why this matters

Timetables and durations are everywhere in real life: catching a bus, baking a cake, timing an exam, or planning a trip with connections. People who can read a timetable quickly never miss a train. People who can add durations never put the cake in for the wrong length of time. And because the whole topic depends on the base-60 nature of time, mastering it also sharpens your general number sense, much like Multi-Step Word Problems.

Try it yourself

Use the bus timetable above to answer these:

1. When does Bus C reach Market Square?
2. How long does Bus B take from High Street to Hospital?
3. You must reach the Hospital by 09:15. Which buses can you catch from the High Street?
4. A film starts at 19:55 and lasts 1 hour 50 minutes — when does it end?

Great work!

You can now find durations by counting on, add a duration to a start time, and read a timetable down its columns and across its rows. Take it further with Time and Calendar Problems.