Fraction calculator
Everything stays in whole numbers until the end, so the answers are exact: a third plus a sixth is exactly a half, not 0.49999999999999994.
Result, lowest terms1/2
- As a mixed number
- 1/2
- As a decimal
- 0.500000
- As a percentage
- 50.0000 %
- Before simplifying
- 9/18
- Common denominator used
- 18
- Reciprocal of the result
- 2/1
The formula
a/b + c/d = (ad + cb)/bd, and the same over a common denominator for subtraction. a/b × c/d = ac/bd. a/b ÷ c/d = ad/bc. The result is then divided through by the greatest common divisor of numerator and denominator.
Worked example
1/3 + 1/6 = (1·6 + 1·3)/18 = 9/18, which divides through by 9 to give 1/2, or 0.5.
How to use it
- 1Enter whole numbers only. For a mixed number like 2¼, use 9/4.
- 2Negative fractions work: put the minus sign on the numerator.
- 3The unsimplified result is shown too, which is what a teacher often wants to see before the cancelling step.
Questions people ask
Why simplify at all?
Because 9/18 and 1/2 are the same number and the second is readable. Convention, and most marking schemes, expect lowest terms.
Why is dividing by a fraction the same as multiplying by its reciprocal?
Dividing asks how many of the second fit into the first. Multiplying by the flipped fraction is the algebraic shortcut: a/b ÷ c/d = a/b × d/c.
Last reviewed: 2026-10-20