How to use the fraction calculator
Type the numerator (top number) and denominator (bottom number) of each fraction, then choose add, subtract, multiply or divide. Negative numbers work in either box. For a mixed number, convert it to an improper fraction first: multiply the whole number by the denominator and add the numerator, so 2 1/3 becomes (2 × 3 + 1)/3 = 7/3.
The rules for each operation
| Operation | Rule | Example |
|---|---|---|
| Add | a/b + c/d = (ad + bc) / bd | 1/2 + 1/3 = 5/6 |
| Subtract | a/b − c/d = (ad − bc) / bd | 3/4 − 1/6 = 7/12 |
| Multiply | a/b × c/d = ac / bd | 2/3 × 9/4 = 3/2 |
| Divide | a/b ÷ c/d = a/b × d/c | 1/2 ÷ 3/4 = 2/3 |
Adding and subtracting need a common denominator; multiplying the two denominators always gives one. Dividing means multiplying by the reciprocal — flip the second fraction upside down.
Worked example: 3/4 + 2/3
- Find a common denominator. The least common denominator of 4 and 3 is 12.
- Rewrite each fraction: 3/4 = 9/12 and 2/3 = 8/12.
- Add the numerators: 9 + 8 = 17, giving 17/12.
- Convert to a mixed number: 12 goes into 17 once with 5 left over, so 17/12 = 1 5/12.
- As a decimal, 17 ÷ 12 = 1.416667 (the 6 repeats).
The calculator multiplies the denominators instead of hunting for the least common one, then reduces at the end. Both routes give the same answer.
Simplifying with the greatest common divisor
A fraction is in lowest terms when the numerator and denominator share no factor other than 1. To get there, divide both by their greatest common divisor (GCD). The calculator finds it with Euclid's algorithm: repeatedly replace the larger number with the remainder of dividing the two. For 84/36: 84 = 2 × 36 + 12, then 36 = 3 × 12 + 0, so the GCD is 12 and 84/36 = 7/3.
Common mistakes
- Adding straight across. 1/2 + 1/3 is not 2/5. Rewrite both with a common denominator first: 3/6 + 2/6 = 5/6.
- Flipping the wrong fraction when dividing. Only the second fraction (the divisor) is inverted.
- Forgetting to simplify. 18/12 is correct but not finished; it reduces to 3/2.
- Zero in the denominator. A fraction with denominator 0 has no value, so the calculator rejects it.
Need a fraction as a percentage? Divide to get the decimal and multiply by 100 — 3/8 = 0.375 = 37.5% — or use the percentage calculator.
Frequently asked questions
How do I enter a mixed number?
Convert it to an improper fraction: multiply the whole number by the denominator and add the numerator. 3 2/5 becomes 17/5. The result is shown as a mixed number again.
How do I enter a whole number?
Use a denominator of 1. To compute 5 − 3/4, enter 5/1 and 3/4; the answer is 17/4, or 4 1/4.
How do I simplify a fraction?
Divide the numerator and denominator by their greatest common divisor. 24/36 has a GCD of 12, so it simplifies to 2/3.
Why is the decimal rounded?
Many fractions, such as 1/3 or 5/12, have decimals that repeat forever. The calculator shows six decimal places; the fraction itself is exact.
Where does the minus sign go in a negative fraction?
In front of the whole fraction. −1/2, 1/(−2) and −(1/2) are the same number, and the calculator always puts the sign on the numerator.
Last updated: October 8, 2026