What you'll learn
Time calculations and timetables involve working with hours and minutes, the 12- and 24-hour clock, and reading and using timetables. In this guide you will learn how to add and subtract time correctly, how to convert between clock formats, how to calculate durations, and how to read bus and train timetables to solve problems. These practical skills appear in functional and problem-solving questions.
Key terms and definitions
24-hour clock — a time format from 00:00 to 23:59 with no am/pm.
12-hour clock — a time format using am (morning) and pm (afternoon/evening).
Duration — the length of time between two moments.
Timetable — a table showing scheduled times, e.g. for buses or trains.
am / pm — before noon / after noon.
Core concepts
Time units
Time uses 60 minutes in an hour and 60 seconds in a minute — not 100 — so calculations are not pure decimals. For example, 1.5 hours is 1 hour 30 minutes, and 90 minutes is 1 hour 30 minutes, not 1.3 hours. Always keep minutes out of 60.
12-hour and 24-hour clock
The 24-hour clock runs 00:00 to 23:59. To convert pm times to 24-hour, add 12 to the hours (3:00 pm → 15:00); am times stay the same (except 12 am = 00:00). To convert 24-hour to 12-hour, subtract 12 from hours of 13 or more and add "pm" (17:30 → 5:30 pm). Midday is 12:00 (12 pm) and midnight is 00:00 (12 am).
Calculating durations
To find a duration, count on from the start time to the end time, often in steps: to the next whole hour, then whole hours, then the remaining minutes. For example, from 09:40 to 11:15: 20 minutes to 10:00, then 1 hour to 11:00, then 15 minutes = 1 hour 35 minutes. Avoid simply subtracting as decimals.
Adding and subtracting time
When adding times, carry over 60 minutes as 1 hour. For example, 2 h 45 min + 1 h 30 min = 3 h 75 min = 4 h 15 min. When subtracting and the minutes are too small, borrow 60 minutes from an hour.
Reading timetables
A timetable lists times in columns (each a journey) and rows (each a stop). To use one, find the relevant stop row and read along to the column for the service you want. Calculate journey durations by finding the difference between the arrival and departure times, and check whether a connection allows enough time.
Worked examples
Example 1: 24-hour conversion
Write 7:25 pm in 24-hour time.
Add 12 to the hours: 7 + 12 = 19, so 19:25.
Example 2: Duration
How long from 14:50 to 16:20?
10 minutes to 15:00, then 1 hour to 16:00, then 20 minutes = 1 hour 30 minutes.
Example 3: Timetable
A bus leaves at 09:48 and arrives at 10:33. How long is the journey?
12 minutes to 10:00, then 33 minutes = 45 minutes.
Common mistakes and how to avoid them
Treating time as decimal. 1.5 hours is 1 h 30 min; minutes are out of 60, not 100.
Wrong am/pm conversion. Add 12 to pm hours; 12 am = 00:00, 12 pm = 12:00.
Subtracting times like decimals. Count up in steps, or borrow 60 minutes when needed.
Reading the wrong timetable column. Follow the correct service column and stop row.
Forgetting to carry 60 minutes. When minutes exceed 60, carry one hour.
Exam technique for Time and Timetables
Keep minutes out of 60, not 100.
Convert clock formats carefully, adding 12 for pm.
Find durations by counting up in steps to the next hour and beyond.
Carry or borrow 60 minutes when adding or subtracting.
Read timetables by matching the stop row to the service column.
Quick revision summary
Time uses 60 minutes per hour, so it is not decimal: 1.5 hours = 1 h 30 min, and 90 minutes = 1 h 30 min. The 24-hour clock runs 00:00–23:59; convert pm times by adding 12 to the hours (7:25 pm → 19:25), with 12 am = 00:00 and 12 pm = 12:00. Find a duration by counting up in steps — to the next whole hour, then whole hours, then the leftover minutes (14:50 to 16:20 = 1 h 30 min) — rather than subtracting like decimals. When adding or subtracting time, carry or borrow 60 minutes. Read a timetable by matching the stop row to the correct service column, and work out journey lengths and connection times from the differences. The common errors are treating time as decimal, wrong am/pm conversions, subtracting like decimals, and misreading timetable columns. Keep minutes out of 60, convert clocks carefully, count up for durations, and read tables methodically.