A complete guide — with formulas and examples — to adding, subtracting, multiplying, and dividing fractions, finding a common denominator, simplifying, and converting to decimals and percents.
A fraction expresses one or more equal parts of a whole. The number above the line is the numerator; the number below the line is the denominator. Fraction calculation covers adding, subtracting, multiplying, and dividing two or more fractions, simplifying the result to lowest terms, and converting it to a decimal or percent. You can also convert between improper fractions and mixed numbers, and compare fractions to see which is larger. The calculator above handles all of these operations in separate tabs, instantly and with a step-by-step explanation.
How do you add and subtract fractions?
Quick answerIf the denominators are already equal, add or subtract the numerators directly. If not, first find a common denominator: take the LCM of the two denominators, expand each fraction to that denominator, then combine the numerators and simplify. For example, 1/2 + 1/3 = 3/6 + 2/6 = 5/6.
- Step 1: Find the least common multiple (LCM) of the denominators.
- Step 2: Expand each fraction to the common denominator — multiply the numerator by (common denominator ÷ its own denominator).
- Step 3: Add or subtract the numerators; the common denominator stays the same.
- Step 4: Simplify by dividing by the GCD of the numerator and denominator.
How do you multiply and divide fractions?
Quick answerMultiplication needs no common denominator: multiply the numerators together and the denominators together (2/3 × 4/5 = 8/15). Division keeps the first fraction, flips the second fraction (its reciprocal), and multiplies (2/3 ÷ 4/5 = 2/3 × 5/4 = 10/12 = 5/6). Simplify the result when possible.
How do you simplify a fraction? (GCD)
Quick answerFind the greatest common divisor (GCD) of the numerator and denominator, then divide both by it. For 8/12, GCD(8,12) = 4, so 8/12 = 2/3. A fraction is fully simplified once the numerator and denominator have no common factor left besides 1.
Converting a fraction to a decimal and percent
Quick answerTo convert a fraction to a decimal, divide the numerator by the denominator (3/4 = 0.75). For a percent, multiply the decimal by 100 (0.75 → 75%). If the division doesn't terminate, the decimal is repeating, and the repeating block is written in parentheses: 1/3 = 0.(3). The "Convert" tab shows the fraction, decimal, and percent forms together.
Improper fractions and mixed numbers
Quick answerA fraction whose numerator is larger than its denominator is an improper fraction (7/4). An improper fraction converts to a mixed number by dividing the numerator by the denominator: the quotient becomes the whole part, and the remainder becomes the new numerator (7/4 = 1 3/4). To reverse the process, multiply the whole part by the denominator and add the numerator (2 1/3 = 7/3).