Number bonds to 10 and 20
Number bonds are pairs of numbers that add to a target: 10's pairs (3+7, 4+6, etc.) and then 20's pairs.
Number bonds to 10 are the most useful number facts in KS1. Children memorise them in Year 1 and use them every day in addition, subtraction and money. Bonds to 20 follow in Year 2.
Worked examples
Bonds to 10: 0+10, 1+9, 2+8, 3+7, 4+6, 5+5, 6+4, 7+3, 8+2, 9+1, 10+0.
Bonds to 20: 1+19, 2+18, 3+17, 4+16, 5+15, 6+14, 7+13, 8+12, 9+11, 10+10.
Use to add: 8 + 5 = 8 + 2 + 3 = 10 + 3 = 13. Bridge through 10 using a bond.
Frequently asked questions
How fast should they recall these?
Year 2 expects instant recall (within 3 seconds) of all bonds to 10 and bonds to 20. Daily quick-fire practice for a week or two usually nails it.
Why bonds to 20 if they know bonds to 10?
Adding 8 + 7 is faster if you know 8 + 7 = 15 directly than if you have to bridge: 8+2+5. Bonds to 20 unlock fluent two-digit arithmetic.
Are subtraction facts the same?
Yes — 10 - 3 = 7 is the same fact as 3 + 7 = 10. Teach them as a fact family.