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Subtraction with time

subtraction

Subtraction with time

Find how long until an event or how much time has passed.

Quick answer

Subtraction with time helps you find out how much time has passed or how long until something happens. You can subtract hours and minutes just like you subtract numbers.

Learning outcome

By the end of this page, you will be able to subtract hours and minutes to find out how much time has passed or how long until an event starts. Success signs:

You can subtract minutes from minutes and hours from hours
You can borrow when minutes are too small
You can solve real-life time subtraction problems
You can explain your thinking when subtracting time

Why this matters

Time subtraction helps you understand how long things take, when events happen, and how to plan your day. Whether you're waiting for your birthday party to start, figuring out how long your football match lasted, or planning your bedtime, subtraction with time is useful every day. It also helps you get better at telling time and working out schedules, which are important life skills.

How it works

Subtracting time is like subtracting numbers, but you have to work with hours and minutes. You can think of it like this:

First, subtract the minutes
If the minutes you're subtracting are more than what you have, you need to borrow from the hours
Then subtract the hours
Put your answer in hours and minutes

Examples you can see

Let's look at a few examples you can imagine or draw. Example 1: Simple subtraction You start your maths homework at 3:15 and finish at 4:00. How long did you work?

Subtract the minutes: 00 - 15 = ?
You can't do this, so you borrow 1 hour (60 minutes) from 4:00
So 4:00 becomes 3:60
Now subtract minutes: 60 - 15 = 45 minutes
Subtract hours: 3 - 3 = 0 hours
Answer: 0 hours and 45 minutes = 45 minutes

Example 2: Real-life situation Your school day starts at 9:00 and ends at 3:30. How long is your school day?

Subtract minutes: 30 - 00 = 30 minutes
Subtract hours: 3 - 9 = ?
You can't do this, so you borrow 1 hour from 3:30
So 3:30 becomes 2:90
Now subtract hours: 2 - 9 = ?
You still can't do this, so you borrow another hour
So 2:90 becomes 1:150
Now subtract hours: 1 - 9 = -8
This is wrong. Let’s think again.
Actually, you want to go from 9:00 to 3:30
So it's 3:30 - 9:00
Subtract minutes: 30 - 0 = 30 minutes
Subtract hours: 3 - 9 = -6
So it's 6 hours less than 12 hours
Answer: 6 hours and 30 minutes

Try it as a mini adventure

Adventure: The Time-Traveling Race You are on a race to find the secret treasure. You start at 10:15 and must reach the treasure before 12:45. How much time do you have to complete your journey?

Step 1: Start time = 10:15
Step 2: End time = 12:45
Step 3: Subtract minutes: 45 - 15 = 30 minutes
Step 4: Subtract hours: 12 - 10 = 2 hours
Step 5: Total time = 2 hours and 30 minutes

You have 2 hours and 30 minutes to complete your race. If you take 1 hour and 50 minutes to reach the first clue, how much time do you have left?

Step 1: Time left = 2 hours 30 minutes
Step 2: Time used = 1 hour 50 minutes
Step 3: Subtract minutes: 30 - 50 = ?
Step 4: Borrow 1 hour = 1 hour 90 minutes
Step 5: Subtract minutes: 90 - 50 = 40 minutes
Step 6: Subtract hours: 1 - 1 = 0 hours
Step 7: Time left = 0 hours 40 minutes = 40 minutes

You have 40 minutes left to find the treasure!

Common mistakes

Mistake: Forgetting to borrow when minutes are too small
Why it happens: Children often forget that they need to borrow from hours when minutes are too small.
Fix: Always check if the minutes you are subtracting are bigger than what you have. If yes, borrow 1 hour (which is 60 minutes) from the hour part.
Mistake: Subtracting hours before minutes
Why it happens: Some children try to subtract hours first, which can cause confusion.
Fix: Always subtract minutes first, then hours. If you need to borrow, do it for minutes first.
Mistake: Thinking that 1 hour = 100 minutes
Why it happens: Children sometimes mix up units and think hours and minutes are the same.
Fix: Remember that 1 hour = 60 minutes. Use a clock or visual aid to help.

Parent and carer guide

Parents and carers can help children with time subtraction by:

Using a real clock to show how time works
Practising subtraction with time using daily events like bedtime or playtime
Encouraging children to draw clocks or use visual aids
Playing games that involve time subtraction, such as planning a trip or cooking
Reinforcing that 1 hour = 60 minutes and that borrowing works the same way as with numbers
Letting children make mistakes and learn from them

Practice questions

Start time: 2:30, End time: 4:15. How much time passed?
Start time: 11:00, End time: 1:45. How much time passed?
Start time: 9:20, End time: 10:50. How much time passed?
Start time: 8:45, End time: 11:20. How much time passed?
Start time: 6:15, End time: 7:50. How much time passed?

Answers:

1 hour 45 minutes
2 hours 45 minutes
1 hour 30 minutes
2 hours 35 minutes
1 hour 35 minutes

FAQ

How do I subtract time when the minutes are smaller?

When the minutes you're subtracting are smaller than what you have, you borrow 1 hour (which is 60 minutes) from the hours part. Then you subtract the minutes.

Can I subtract time like regular numbers?

Yes, but you must remember that 1 hour = 60 minutes. If you need to borrow, you borrow 60 minutes from the hours.

Why do I need to borrow from hours?

You borrow from hours when the minutes you're subtracting are more than what you have. This makes it possible to subtract the minutes properly.

How can I practice time subtraction?

You can practice by looking at clocks, solving time problems from daily life, or playing games that involve time.

What if I get confused with time subtraction?

It's normal to get confused at first. Use a clock, draw pictures, or ask a parent or teacher for help. Practice makes progress!