Add & Subtract to 20
Learn how to add and subtract any two numbers when the answer or starting number is 20 or less.
Reading is good — doing is better. Practice Add & subtract to 20 as an interactive lesson.
Practice freeDefinition
Adding means putting two groups of things together to find how many in all. Subtracting means taking away some things from a group to find how many are left. When we add or subtract to 20, all the numbers we use are between 0 and 20.
Remember the rule
Start BIG, count on to ADD; start BIG, count back to SUBTRACT.
Key words
- Add
- Put two amounts together to get a bigger total.
- Subtract
- Take away one amount from another to get a smaller number.
- Sum
- The answer you get after adding two numbers together.
- Difference
- The answer you get after subtracting one number from another.
- Equals
- Means 'is the same as'; shown by the = sign.
- Number bond
- A pair of numbers that add up to make one bigger number, like 7 and 3 make 10.
- Fact family
- A set of related addition and subtraction facts using the same three numbers, like 6+4=10, 4+6=10, 10-4=6, and 10-6=4.
- Count on
- Start at the bigger number and count forward to add instead of starting from 1.
Worked examples
8 + 5 = ?
→ 13 · Count on from 8: 9, 10, 11, 12, 13 — that's 5 more steps.
14 - 6 = ?
→ 8 · Count back from 14: 13, 12, 11, 10, 9, 8 — that's 6 steps back.
7 + 7 = ?
→ 14 · Doubles are easy to memorize: 7 + 7 is always 14.
20 - 9 = ?
→ 11 · Think: 9 + ? = 20. Count on from 9 until you reach 20 — that's 11 steps.
6 + 8 = ?
→ 14 · Make a 10 first: 6 + 4 = 10, then add the leftover 4 to get 14.
15 - 7 = ?
→ 8 · Use the fact family: if 7 + 8 = 15, then 15 - 7 = 8.
Common mistakes
- Counting the starting number when counting on — for 8+5, kids say '8,9,10,11,12' and get 12 instead of 13. Always start counting AFTER the big number.
- Mixing up addition and subtraction symbols — slow down and check whether the problem says + or -.
- Forgetting that subtraction is not commutative — 10-3 is 7, but 3-10 does not work the same way with the numbers kids use.
- Skipping numbers when counting back, especially crossing a ten like going from 12 to 9.
- Not using what they know — if a child knows 8+8=16, they can figure out 8+9=17 by just adding one more.
FAQs
What does 'within 20' mean?
It means the numbers in the problem and the answer are all between 0 and 20. For example, 13 - 5 = 8 is within 20, but 25 - 3 is not.
How can my child memorize addition facts faster?
Practice a little every day. Focus on one group at a time: doubles first (3+3, 4+4), then making tens (8+2, 7+3). Short, daily practice beats one long session.
What is 'making a 10' and why does it help?
Making a 10 means breaking a number apart so you can reach 10 first. For example, 9+6: take 1 from the 6 to make 9+1=10, then add the leftover 5 to get 15. Ten is easy to work with.
My child counts on fingers — is that okay?
Yes, especially at the start of 1st grade. Fingers are a great tool. Gently encourage moving toward counting on in their head as they grow more confident.
How does subtraction relate to addition?
They are opposites. Every subtraction problem has a matching addition fact. If your child knows 6+7=13, they already know 13-7=6 and 13-6=7. Teach fact families together.
What if my child gets the wrong answer — how should I help?
Ask them to act it out with small objects like pennies or blocks. Seeing real objects they can move helps make the math concrete and fixes the confusion better than just telling them the right answer.
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