LCM Calculator
Find the least common multiple of two or more numbers — the smallest value they all divide into — with prime factorisations shown.
How to use it
- Enter the numbers separated by commas, spaces or new lines.
- For more than two numbers the LCM is built up one pair at a time.
- Use it to find a common denominator when adding fractions.
Examples
| 4, 6 | LCM 12 |
| 12, 18, 30 | LCM 180 |
The least common multiple is the smallest number that every value in the list divides into. Where GCF answers 'what's the biggest shared group', LCM answers 'when do these things next line up' — the classic use is finding a common denominator, but it also solves real scheduling problems.
Worked example — scheduling
Bus A leaves a stop every 12 minutes and Bus B leaves the same stop every 18 minutes; both left together at 8:00am. They next leave together after LCM(12, 18) = 36 minutes — at 8:36am. Add a third route on a 30-minute cycle and all three next align after LCM(12, 18, 30) = 180 minutes, three hours later.
LCM and fractions
Adding 1/12 + 1/18 needs a common denominator — the lowest one is LCM(12, 18) = 36. Rewritten as 3/36 + 2/36, the fractions add directly to 5/36. Using any larger common multiple works too, but the numbers get needlessly big.
Questions people ask
How do I use the LCM to add fractions?
The LCM of the denominators is the lowest common denominator. Rewrite each fraction over that denominator, then add the numerators.
Is anything sent to a server?
No. Every calculation runs in your browser, so nothing you type is uploaded and the page keeps working offline once it has loaded.
Last updated 17 August 2026