How do you add fractions with different denominators?

Find the lowest common denominator (LCD) of both fractions. Convert each fraction to an equivalent fraction with the LCD. Add the numerators and keep the LCD as the denominator. Simplify by dividing both parts by their greatest common divisor (GCD).

What is a lowest common denominator?

The lowest common denominator (LCD) is the smallest number that both denominators divide into evenly. For example, the LCD of 1/4 and 1/6 is 12, because 12 is the smallest number divisible by both 4 and 6.

Why is my answer an improper fraction?

The calculator returns a simplified numerator over denominator, so 3/4 + 2/3 shows as 17/12 with the decimal 1.416667. As a mixed number that is 1 5/12: 17 divided by 12 is 1 remainder 5.

Can I add a whole number to a fraction?

Write the whole number over 1: 3 + 1/4 is entered as 3/1 + 1/4, which gives 13/4 (3.25).

Add fractions calculator

Add two fractions with any denominators. Enter the numerators and denominators for each fraction and this calculator finds the common denominator, adds the fractions, and simplifies the result. Step-by-step working is shown so you can see exactly how the answer was reached. All calculations run locally in your browser.

How it works

To add 3/4 and 2/3, the calculator finds the least common multiple of the denominators (12), rewrites both fractions over it (9/12 and 8/12) and adds the numerators to get 17/12. The greatest common divisor of 17 and 12 is 1, so 17/12 is already in lowest terms, shown with its decimal value 1.416667. All arithmetic runs in JavaScript in your browser.

Processing runs in your browser

All calculations happen locally in your browser tab. Our servers are not involved at any point.

Related operations

For converting a fraction into a percentage, try the percentage calculator. To switch between metric and imperial measures, use the unit converter. For translating numbers into Roman numerals, see the Roman numeral converter.

Frequently asked questions

How do you add fractions with different denominators?: Find the lowest common denominator (LCD) of both fractions. Convert each fraction to an equivalent fraction with the LCD. Add the numerators and keep the LCD as the denominator. Simplify by dividing both parts by their greatest common divisor (GCD).
What is a lowest common denominator?: The lowest common denominator (LCD) is the smallest number that both denominators divide into evenly. For example, the LCD of 1/4 and 1/6 is 12, because 12 is the smallest number divisible by both 4 and 6.
Why is my answer an improper fraction?: The calculator returns a simplified numerator over denominator, so 3/4 + 2/3 shows as 17/12 with the decimal 1.416667. As a mixed number that is 1 5/12: 17 divided by 12 is 1 remainder 5.
Can I add a whole number to a fraction?: Write the whole number over 1: 3 + 1/4 is entered as 3/1 + 1/4, which gives 13/4 (3.25).

Last reviewed September 30, 2026

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