The least common denominator of two fractions is the least common multiple of the fractions' denominators.

In the example above, it's found by multiplying the denominators, $3\cdot 2=6.$ Sometimes, the least common denominator (LCD), is lower than multiplying the denominators. For example, $$\frac{5}{6}+\frac{1}{4},$$ has the least common denominator $12$ since $6\cdot 2=12$ and $4\cdot 3=12.$