Mental Maths Tricks

Fast, reliable ways to do everyday maths in your head, with simple steps and an explanation of why each method works.

⚡ Fastest MethodEnter a calculation and see whether there is a useful mental shortcut. × Fast MultiplicationUseful shortcuts for ×5, ×9, ×11, ×25, ×50, ×99 and more. % Fast PercentagesBuild awkward percentages from easy ones and use percentage symmetry. x² Fast SquaresSquare numbers ending in 5 or numbers close to 100. +− Fast Add & SubtractRound, compensate and use complements to make arithmetic easier. ÷ Fast DivisionSimple transformations for ÷5, ÷25, ÷50 and powers of two. ✓ Divisibility TestsQuickly test divisibility by 2, 3, 4, 5, 6, 8, 9, 10 and 11. ½ Fractions ↔ Decimals ↔ %Learn the common equivalents worth knowing by sight. ≈ Estimate & CheckQuickly decide whether an answer is in the right ballpark.

Simple, not magical

These methods are mathematical identities or clearly stated shortcuts. Each page shows the answer first, the quick method second, and a short explanation of why it works.