How to use the fraction calculator
- Add, subtract, multiply, divide: type two fractions, mixed numbers, whole numbers or decimals, such as 3/4, 1 1/2, −2/5, 4 or 0.75. Leave a space between the whole number and the fraction in a mixed number.
- Simplify or convert: type one fraction or decimal to get it in simplest form, as a mixed number, a decimal (with repeating digits marked) and a percentage.
Fractions are always exact: the calculator works with whole numbers throughout. Decimals and percentages are rounded only for display, and repeating digits are marked with a line.
Fraction rules
a/b + c/d = (a×d + c×b) / (b×d)
a/b − c/d = (a×d − c×b) / (b×d)
a/b × c/d = (a×c) / (b×d)
a/b ÷ c/d = a/b × d/c
After each step, the result is simplified by dividing the top and bottom by their greatest common factor. For adding and subtracting, the working uses the lowest common denominator, which keeps the numbers small.
Worked example
1 1/2 + 2/3: 1 1/2 = 3/2. The lowest common denominator of 2 and 3 is 6, so 3/2 = 9/6 and 2/3 = 4/6. 9/6 + 4/6 = 13/6, which is 2 1/6, or 2.16 as a decimal.
Simplify 18/24: the greatest common factor of 18 and 24 is 6, so 18/24 = 3/4 = 0.75 = 75%.
Repeating decimals
Some fractions never end as decimals. 1/3 = 0.333… and 1/7 = 0.142857142857…. A line over the digits shows the part that repeats: 1/7 = 0.142857. A fraction gives a terminating decimal only when its simplified denominator has no prime factors other than 2 and 5.
For percentages of numbers, use the percentage calculator.
Frequently asked questions
How do I type a mixed number?
Put a space between the whole number and the fraction: 2 3/8. For a negative mixed number, put the minus sign first: −2 3/8.
Can I enter a decimal?
Yes. 0.375 is read exactly as 375/1000 and simplified to 3/8.
Formulas checked 29 October 2026. How we test our calculators. Check important results, and show your own working where your teacher or exam asks for it.