Number Bonds
Free number bonds game: find the missing number that makes 20 (7 + ? = 20). Builds the make-ten skill 1st and 2nd graders need. No sign-up.
Grade 1–2 · Free · No sign-up
How to play & why it works
Each round shows a bond with a hole in it — 7 + _ = 20, 13 + _ = 20 — and you type the missing number. It is the classic number-bonds exercise, served fast enough to build real recall instead of finger-counting.
Number bonds (the pairs that make 10, then 20, then 100) are the backbone of mental arithmetic. Every "make a ten" strategy — the single most useful trick in elementary addition — depends on knowing the pairs to 10 and 20 cold.
Work the tens first: 1+9, 2+8, 3+7, 4+6, 5+5. Once those are automatic, the pairs to 20 follow the same pattern one ten higher, and the drill will make the connection obvious by mixing them.
In the free MathIt app the bonds ladder continues to 100 and 1000, feeding into a full mental-math curriculum with adaptive difficulty, streaks and family battles.
Number bonds are the hinge between counting and calculating. A child who instantly knows that 7 needs 3 more to make 10 can use that everywhere: 7 + 5 becomes 7 + 3 + 2, 23 + 8 becomes 23 + 7 + 1. Without them, every sum stays a counting exercise.
Bonds to 10 come first and matter most, because the base-ten system is built on them. Bonds to 20 follow naturally once the first set is automatic. If a child hesitates on bonds to 10, that is the thing to practise — not the larger sums that depend on them.
Skills you'll practice
Keep practicing
Frequently asked questions
What are number bonds?
A number bond is a pair that makes a target number — 3 and 7 make 10, 6 and 14 make 20. They are usually shown with one part missing, which is why they are also called missing-addend problems.
Why do schools teach number bonds instead of just addition?
Because bonds are what make mental arithmetic possible. Knowing pairs to 10 lets a child bridge through ten instead of counting, which is the single biggest speed gain in early arithmetic.
What age should a child know their bonds to 10?
Most curricula expect fluency by the end of first grade, around age 6 or 7. Bonds to 20 usually follow within the next year.
Get the full game
Adaptive difficulty, daily streaks, and live 2–5 player math battles — free on iOS and Android.