Find the LCD
Least common denominator, step by step.
Enter two fractions and get their least common denominator, with both fractions rewritten over it.
The steps
Result
See it
The least common denominator (LCD) is the least common multiple of the denominators. It's the smallest bottom number both fractions can share, which is what you need before adding or subtracting.
FractionSteps finds the LCD and rewrites both fractions over it.
Worked examples
3 and 4
LCD = 12
6 and 4
LCD = 12
2 and 5
LCD = 10
8 and 12
LCD = 24
Frequently asked
What is the least common denominator?
It is the smallest number that both denominators divide into evenly — the least common multiple of the denominators.
Why do I need the LCD?
Adding or subtracting fractions requires a shared denominator. Using the least one keeps the numbers as small as possible.
Is the LCD always the product of the denominators?
Not always. For 6 and 4 the product is 24, but the LCD is only 12, because they share a common factor.