Finds the lowest common denominator of two fractions and rewrites both fractions over that shared denominator.
How it works
The least common multiple of both denominators becomes the common denominator, and each numerator is scaled to match.
What this does not include
This does not include combining the two fractions into a single sum or difference — for full fraction arithmetic, use this site’s fraction calculator instead.
How to use this calculator
- Enter both fractions’ numerators and denominators.
Frequently asked questions
Why do fractions need a common denominator to be added?
Because a fraction’s numerator only makes sense relative to its own denominator — matching the denominators first makes the numerators directly comparable and combinable.
Is the lowest common denominator the only valid common denominator?
No — any common multiple of both denominators would work, but the lowest one keeps the numbers as small and simple as possible.
What if the two denominators are already the same?
The common denominator is just that shared value, and neither numerator needs to be rescaled.
