How to Add, Subtract, Multiply and Divide Fractions

Use a common denominator to understand a result instead of treating the answer as a black box.

Use the Fraction Calculator alongside this illustrative example.

A practical example

Adding 1/2 and 1/3 gives 3/6 + 2/6 = 5/6. A useful rough check is that the answer must be greater than 1/2 and less than 1. For division, 1/2 ÷ 1/3 equals 3/2 because there are one and a half one-third portions in one half.

Check the result

Convert a mixed number such as 1 1/2 to 3/2 before using separate numerator and denominator fields. Keep a negative sign with the value rather than entering it into both parts.

Try a comparison

Compare 1/2 + 1/3 with 1/2 × 1/3. The sum is 5/6 but the product is 1/6. A product smaller than either input is expected when multiplying positive fractions below one; it is not automatically a calculator error.

What this does not establish

A denominator of zero is undefined. For quantities in a recipe or plan, confirm that both fractions describe the same unit before combining them.

Report unclear guidance or a result that needs checking.