X Tables
Number Sense

Number bonds to 20

Extend known facts to 20 using tens, ones and related facts.

Quick answer

Number bonds to 20 are pairs of numbers that add together to make 20, like 10 + 10, 15 + 5, or 12 + 8. You can use what you know about number bonds to 10 to help you find number bonds to 20.

Learning outcome

By the end of this page, you will be able to find number bonds to 20 using what you already know about number bonds to 10. Success signs:
  • You can quickly say what number you need to add to 13 to make 20
  • You can use number bonds to 10 to help you find bonds to 20
  • You can find number bonds to 20 by counting up from one number
  • You can check if two numbers make 20

Why this matters

Number bonds to 20 are important because they help you add and subtract numbers more quickly and easily. When you know that 13 + 7 = 20, you can quickly work out that 20 - 13 = 7. This helps with mental maths and problem-solving in everyday life. You'll use number bonds to 20 when sharing snacks, counting money, or solving puzzles.

How it works

Number bonds to 20 are pairs of numbers that add together to make 20. There are many ways to find them:
  • Use what you know about number bonds to 10
  • Count up from one number
  • Use objects or drawings
Let's look at each way in more detail. Using what you know about number bonds to 10: If you know that 7 + 3 = 10, then you also know that 17 + 3 = 20 because 17 is 10 more than 7. Counting up: If you have 14, count up to 20: 15, 16, 17, 18, 19, 20. That's 6 more, so 14 + 6 = 20. Using objects or drawings: You can use counters, blocks, or draw circles to help you see how many more you need.

Examples you can see

Let's look at some examples of number bonds to 20: Example 1: Using number bonds to 10 If you know that 8 + 2 = 10, then you also know that 18 + 2 = 20. Because 18 is 10 more than 8, and you're adding 2 to both, the total is 10 more too. Example 2: Counting up If you have 11, count up to 20: 12, 13, 14, 15, 16, 17, 18, 19, 20. That's 9 more, so 11 + 9 = 20. Example 3: Drawing to help Draw 13 circles and then draw 7 more circles. Count them all together. 13 + 7 = 20.

Try it as a mini adventure

Adventure: The Number Bond Treasure Hunt You are on a treasure hunt in a magical garden. You need to find 20 golden coins to unlock the treasure chest. You've already found 12 coins. How many more coins do you need? Step 1: You know you have 12 coins. Step 2: You need 20 coins in total. Step 3: Count up from 12 to 20: 13, 14, 15, 16, 17, 18, 19, 20. Step 4: That's 8 more coins you need. So 12 + 8 = 20. Let's try another one: Step 1: You have 16 coins. Step 2: You need 20 coins. Step 3: Count up from 16 to 20: 17, 18, 19, 20. Step 4: That's 4 more coins you need. So 16 + 4 = 20.

Common mistakes

  • Mistake: Thinking 14 + 6 = 20 because 14 + 6 = 20, but forgetting to double-check. Why it happens: Rushing through the problem or not using a strategy. Fix: Use a drawing or counting strategy to check your answer.
  • Mistake: Using 10 + 10 = 20 and thinking that's the only way to make 20. Why it happens: Not understanding that there are many number bonds to 20. Fix: Try to find different pairs of numbers that add to 20.
  • Mistake: Counting down instead of up when looking for number bonds. Why it happens: Confusion about which direction to count. Fix: Always count up from the number you have to 20.

Parent and carer guide

Help your child learn number bonds to 20 by:
  • Practising with everyday objects like counters, buttons, or toys
  • Using number bonds to 10 to help them think about number bonds to 20
  • Playing games like "What's the missing number?"
  • Using real-life examples like sharing snacks or counting money
  • Encouraging them to use drawings or physical counting to check their answers
Remember, learning number bonds takes time. Be patient and celebrate small successes. Don't worry if they make mistakes – that's how they learn!

Practice questions

  1. What number do you add to 15 to make 20?
  2. Find a number bond to 20 for 9 + ? = 20
  3. Use counting up to find what number you need to add to 17 to make 20
  4. What is 20 - 13?
  5. Which of these pairs makes 20: 11 + 9 or 12 + 8?
Answers:
  1. 5
  2. 11
  3. 3
  4. 7
  5. Both pairs make 20

FAQ

What are number bonds to 20?

Number bonds to 20 are pairs of numbers that add together to make 20, like 10 + 10, 15 + 5, or 12 + 8.

How can I help my child learn number bonds to 20?

You can use objects like counters or blocks, play games, use drawings, or think about real-life examples like sharing snacks or counting money.

Why are number bonds important?

Number bonds help you add and subtract numbers quickly. They are useful for mental maths and solving problems in everyday life.

Can I use number bonds to 10 to help with number bonds to 20?

Yes! If you know that 7 + 3 = 10, then you also know that 17 + 3 = 20 because 17 is 10 more than 7.

How many number bonds to 20 are there?

There are 21 number bonds to 20. These include 0 + 20, 1 + 19, 2 + 18, and so on up to 20 + 0.