Subtracting within 20
Counting back, finding the difference, and subtracting using a known addition fact.
Year 1 introduces subtraction as ‘take away’. Year 2 broadens the meaning to include ‘finding the difference’ (which is often the trickier one).
Worked examples
Take away (count back): 12 - 3 = ? Start at 12, count back 11, 10, 9. Answer 9.
Find the difference: 8 and 11 are how far apart? Count up from 8: 9, 10, 11 = 3.
Use addition: 15 - 7 = ? Think ‘7 + ? = 15’ → ? = 8.
Frequently asked questions
Why two strategies?
Counting back works for small differences (e.g. 20 - 2). Counting up is faster for close-ish numbers (e.g. 11 - 8 takes 3 steps up vs 8 down).
Should I write subtraction left-to-right or right-to-left?
Year 1/2 work mentally and with number lines — not column subtraction. Vertical column method comes in Year 3.
Negative numbers?
KS1 stays at zero or above. Negative numbers come in Year 4.