Fraction calculator
Works with proper fractions, improper fractions and mixed numbers. You get the answer in its simplest form, as a mixed number and as a decimal — with the working shown so you can check homework or recipes.
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Adding and subtracting fractions
You can only add or subtract fractions once the bottom numbers (denominators) match. Find the lowest common denominator, rewrite each fraction over it, then add or subtract the tops:
1/2 + 3/4: the lowest common denominator of 2 and 4 is 4. 1/2 = 2/4, so 2/4 + 3/4 = 5/4 = 1 1/4.
5/6 − 1/4: the lowest common denominator of 6 and 4 is 12. 5/6 = 10/12 and 1/4 = 3/12, so 10/12 − 3/12 = 7/12.
We go through more examples, including the shortcut for tricky denominators, in how to add fractions with different denominators.
Multiplying and dividing fractions
Multiplying is the easy one: multiply the tops, multiply the bottoms. 2/3 × 3/5 = 6/15 = 2/5. You don't need a common denominator.
To divide, flip the second fraction upside down (its reciprocal) and multiply. 3/4 ÷ 1/2 = 3/4 × 2/1 = 6/4 = 1 1/2. The school rhyme is "keep, change, flip". Step-by-step examples are in how to multiply and divide fractions.
Working with mixed numbers
Turn a mixed number into an improper fraction before you do anything else: multiply the whole number by the denominator and add the numerator. 2 3/8 becomes (2 × 8 + 3)/8 = 19/8. Do the sum, then convert back at the end by dividing: 19 ÷ 8 = 2 remainder 3, so 2 3/8.
The most common mistake with mixed numbers is multiplying the whole numbers and fractions separately. 1 1/2 × 1 1/2 is not 1 1/4; it's 3/2 × 3/2 = 9/4 = 2 1/4.
How to simplify a fraction
Divide the top and bottom by their greatest common divisor (the biggest number that divides both). For 18/24, the GCD is 6, so 18/24 = 3/4. If you can't spot the GCD, keep dividing by small primes (2, 3, 5, 7) until nothing else goes in evenly. The calculator always shows the fully simplified answer and the number it divided by.
Common fractions as decimals and percentages
| Fraction | Decimal | Percent |
|---|---|---|
| 1/2 | 0.5 | 50% |
| 1/3 | 0.333… | 33.3% |
| 1/4 | 0.25 | 25% |
| 1/5 | 0.2 | 20% |
| 1/8 | 0.125 | 12.5% |
| 3/8 | 0.375 | 37.5% |
| 2/3 | 0.666… | 66.7% |
| 3/4 | 0.75 | 75% |
To go the other way, the "decimal to fraction" box above writes the decimal over a power of ten and simplifies: 0.375 = 375/1000 = 3/8. There's a full guide in converting between fractions, decimals and percentages, and the percentage calculator handles percentage questions directly.
Frequently asked questions
How do you add fractions with different denominators?
Find the lowest common denominator, rewrite both fractions over it, then add the numerators. For example 1/3 + 1/4 = 4/12 + 3/12 = 7/12.
How do you divide fractions?
Flip the second fraction and multiply. For example 2/3 ÷ 4/5 = 2/3 × 5/4 = 10/12 = 5/6.
How do you simplify a fraction?
Divide the numerator and denominator by their greatest common divisor. 12/16 has a GCD of 4, so it simplifies to 3/4.
How do I enter a mixed number?
Put the whole number in the first box, the numerator in the second and the denominator in the third. For 2 1/3, enter 2, 1 and 3.
How do I convert a fraction to a decimal?
Divide the top by the bottom. 3/8 = 3 ÷ 8 = 0.375. Multiply by 100 to get a percentage: 37.5%.
Results are exact for whole-number inputs. Very large numerators or denominators may lose precision in the decimal display.