GCD & LCM Calculator

About this calculator

This calculator finds the greatest common divisor (GCD) — the largest number that divides both inputs evenly — and the least common multiple (LCM) — the smallest number that both inputs divide into evenly — for two integers, using the Euclidean algorithm under the hood.

GCD is used to reduce a fraction to its simplest form (dividing numerator and denominator by their GCD) and comes up in scheduling problems, like finding the largest even group size two teams can both be split into. LCM is used to find a common denominator when adding or subtracting fractions, and to solve 'when do these two repeating events line up again' problems, like two buses that pass a stop every 12 and 18 minutes. Students working through math homework and anyone solving a scheduling or fraction problem by hand use this to check their work quickly.