Formula
a/b + c/d = (a·d + c·b) / (b·d) (or use the least common denominator)a/b − c/d = (a·d − c·b) / (b·d)a/b × c/d = (a·c) / (b·d)a/b ÷ c/d = (a·d) / (b·c) How it works
To add or subtract fractions, they first need the same denominator. This calculator uses the least common denominator — the smallest number both denominators divide into — which keeps the numbers small. Once the bottoms match, you simply add or subtract the tops.
Multiplying is easier: multiply the numerators together and the denominators together. To divide, flip the second fraction upside down (take its reciprocal) and multiply.
Every answer is reduced to lowest terms by dividing the numerator and denominator by their greatest common factor. If the result is larger than 1, it is also shown as a mixed number — a whole number plus a proper fraction — which is how many textbooks expect final answers.
Frequently asked questions
How do I enter a mixed number like 2 1/3?
Convert it to an improper fraction first: multiply the whole number by the denominator and add the numerator. 2 1/3 becomes (2 × 3 + 1)/3 = 7/3.
How do I enter a negative fraction?
Put the minus sign on the numerator, for example −3 over 4. The calculator keeps the sign on the numerator in the answer.
Why do I flip the second fraction when dividing?
Dividing by a number is the same as multiplying by its reciprocal. Dividing by 3/4 asks “how many 3/4s fit?”, which equals multiplying by 4/3.