Adding fractions needs a common denominator.
About this calculator
Adding fractions needs a common denominator. The least common denominator (LCD) is the smallest number every denominator divides into — it is the LCM of the denominators.
Enter fractions separated by commas, like 1/2, 1/3, 1/4. The LCD of 2, 3, and 4 is 12. One-half becomes 6/12, one-third becomes 4/12, and one-quarter becomes 3/12.
Use [[compare-fractions]] to order fractions after converting. Simplify results with [[simplify-fractions]]. For two-number LCM see [[lcm]].
Common uses
- Find a common denominator before adding fractions
- Rewrite unlike fractions for comparison
- Check homework LCD steps quickly
- Prepare fractions for addition in recipes or budgets
Frequently asked questions
What is the LCD of 1/2, 1/3, and 1/4?
12. LCM(2, 3, 4) = 12. The fractions become 6/12, 4/12, and 3/12.
Is LCD the same as LCM?
For fractions, yes — the LCD is the LCM of the denominators. LCM applies to whole numbers; LCD names that LCM when used as a denominator.
Can I enter whole numbers?
Yes. A whole number like 2 is treated as 2/1. Its denominator 1 does not change the LCD of the other fractions.
How is LCD different from simplifying?
LCD makes denominators match for addition. Simplifying reduces a single fraction to lowest terms after you compute the result.