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Free Online LCD Calculator

Enter fractions such as 1/2, 1/3 separated by commas. You get the least common denominator—the smallest number all denominators divide into.

The least common denominator (LCD) is the smallest number all denominators divide into. You need it before adding or subtracting fractions with different bottoms.

Try an example

How the LCD calculator works

The least common denominator (LCD) is the least common multiple (LCM) of the denominators. You need it before adding or subtracting fractions with different bottoms: rewrite each fraction with the LCD, then combine numerators.

For 1/2 and 1/3 the LCD is 6. Then 1/2 = 3/6, 1/3 = 2/6, and 3/6 + 2/6 = 5/6.

Worked examples

Real problems you might enter in the calculator above, with short walkthroughs.

  • LCD for 1/2 and 1/3

    LCM of 2 and 3 is 6. Use sixths to add: 3/6 + 2/6 = 5/6.

    Fractions1/21/3LCD6

  • Three fractions

    24 is the smallest number that 4, 6, and 8 all divide into.

    Fractions3/45/67/8LCD24

  • Adding 1/4 and 1/6

    Rewrite as 3/12 + 2/12 = 5/12.

    Fractions1/41/6LCD12

  • Comparing 2/5 and 3/7

    With denominator 35 you can compare 14/35 and 15/35 to see that 3/7 is larger.

    Fractions2/53/7LCD35

Frequently asked questions about the lCD Calculator

  • What is the LCD?

    The least common denominator is the smallest number that every denominator in your list divides into evenly. It lets you add or subtract fractions on the same bottom.

  • How is LCD related to LCM?

    The LCD of a set of fractions is the LCM of their denominators.

  • How do I add 1/4 and 1/6?

    LCD is 12. Convert to 3/12 + 2/12 = 5/12.

  • Why not just multiply the denominators?

    Multiplying denominators always works but often gives a larger common denominator than you need. The LCD is the smallest shared bottom.