How the fraction calculator works
Type each fraction as a whole number, a top number (numerator) and a bottom number (denominator). For a mixed number like 1½, put 1 in the whole number box, 1 on top and 2 on the bottom. For an ordinary fraction such as ⅔, leave the whole number blank. Pick add, subtract, multiply or divide and the answer appears straight away, simplified, with each step of the working shown so you can follow it or copy it into homework.
The rules for each sum
Adding and subtracting fractions
You can only add or subtract fractions when the bottom numbers are the same. Find the lowest common denominator (the smallest number both bottoms divide into), convert each fraction, then add or subtract the tops and keep the bottom.
a/b + c/d = (a × (L ÷ b) + c × (L ÷ d)) / L, where L is the lowest common multiple of b and d
Multiplying fractions
Multiply the top numbers together and the bottom numbers together. There's no need for a common denominator.
a/b × c/d = (a × c) / (b × d)
Dividing fractions
Flip the second fraction upside down (find its reciprocal), then multiply. People often remember this as "keep, change, flip".
a/b ÷ c/d = a/b × d/c = (a × d) / (b × c)
Mixed numbers and simplifying
Before any sum, turn mixed numbers into improper fractions: multiply the whole number by the bottom and add the top. So 2⅓ is (2 × 3 + 1)/3 = 7/3. At the end, simplify by dividing the top and bottom by their highest common factor, and turn an improper fraction back into a mixed number by dividing the top by the bottom.
Worked examples
1½ + ⅔
1½ = 3/2. The lowest common denominator of 2 and 3 is 6, so 3/2 = 9/6 and 2/3 = 4/6. 9 + 4 = 13, giving 13/6. As a mixed number that's 2⅙, or 2.1667 as a decimal.
¾ − ⅙
The lowest common denominator of 4 and 6 is 12. ¾ = 9/12 and ⅙ = 2/12, so the answer is 7/12 (0.5833).
2⅓ × 3/7
2⅓ = 7/3. Multiply: (7 × 3)/(3 × 7) = 21/21, which simplifies to 1.
⅝ ÷ 1¼
1¼ = 5/4. Flip it to get 4/5, then multiply: (5 × 4)/(8 × 5) = 20/40. Dividing top and bottom by 20 gives ½.
Common fractions as decimals and percentages
| Fraction | Decimal | Percentage |
|---|---|---|
| 1/2 | 0.5 | 50% |
| 1/3 | 0.3333 (recurring) | 33.33% |
| 1/4 | 0.25 | 25% |
| 1/5 | 0.2 | 20% |
| 1/8 | 0.125 | 12.5% |
| 2/3 | 0.6667 (recurring) | 66.67% |
| 3/4 | 0.75 | 75% |
| 3/8 | 0.375 | 37.5% |
Where fractions come up
- Recipes: scaling ¾ of a cup up by 1½ times is ¾ × 3/2 = 9/8, or 1⅛ cups. Our cooking conversion calculator turns cups into grams.
- DIY: imperial measurements such as 5/8 inch drill bits and 3/4 inch timber.
- Money: "a third off" is a fraction too. To work out discounts as percentages, use the percentage calculator or the discount calculator.
- Homework: the steps follow the methods taught in UK schools for GCSE maths, so you can check your own working line by line.
Frequently asked questions
How do you add fractions with different denominators?
Find the lowest common denominator, convert both fractions, then add the tops. For 1/4 + 1/6, the lowest common denominator is 12, so it's 3/12 + 2/12 = 5/12.
How do you divide fractions?
Flip the second fraction and multiply. 2/3 ÷ 4/5 = 2/3 × 5/4 = 10/12, which simplifies to 5/6.
How do you turn a mixed number into an improper fraction?
Multiply the whole number by the bottom number and add the top. 3⅖ is (3 × 5 + 2)/5 = 17/5.
How do you simplify a fraction?
Divide the top and bottom by their highest common factor. 18/24 has a highest common factor of 6, so it simplifies to 3/4.
What is 1/3 as a decimal?
1/3 is 0.3333 recurring, or 33.33% to two decimal places.
Last reviewed October 2026 using 2026/27 figures. This calculator gives an estimate for guidance only.