The rule: add the numerators
To add two fractions that have the same denominator, the rule fits in one sentence: add the numerators, and keep the denominator unchanged.
25 + 15 = 35
2 + 1 = 3 on top; the denominator 5 stays the same
- Check that both fractions have the same denominator.
- Add the two numerators together.
- Copy the common denominator down, without changing it.
Why the denominator doesn't move
The denominator shows the size of the parts (how many pieces the whole was cut into). Two fractions with the same denominator are therefore talking about parts of the same size: adding 2 fifths and 1 fifth is like adding 2 apples and 1 apple — the answer is in apples, not "half-apples".
2/5 (2 parts) + 1/5 (1 part) = 3/5 (3 parts) — the parts stay the same size
Adding using a number line
A number line helps you picture the addition as a movement: start at 0, move forward by the first fraction, then forward again by the second.
For 1/6 + 3/6 on a number line marked in sixths: start at 0, move forward 1 mark (→ 1/6), then forward 3 more marks (→ 4/6). You land on the mark 4/6, exactly the result of the addition.
When the result is more than 1 whole
If the sum of the numerators becomes equal to or bigger than the denominator, the result is more than one whole.
34 + 24 = 54 = 1 + 14
5/4 is 4/4 (1 whole) plus 1/4 left over
We say that 5/4 is a fraction greater than 1: it represents more than one complete whole.
Simplifying the result
Once the addition is done, always check whether the fraction obtained can be simplified, by dividing the numerator and denominator by a common factor.
2/8 + 2/8 = 4/8 = 1/2
4/8 simplifies by dividing by 4: numerator and denominator ÷ 4
Mistakes to avoid
- Adding the denominators as well as the numerators — mistake number one.
- Trying to add two fractions that don't have the same denominator using this method (they must first be given the same denominator).
- Forgetting to simplify the final result when possible.
Worked exercises
3/8 + 2/8
4/6 + 3/6
1/6 + 2/6, simplified
Now it's your turn!
On EasyMaths, your child practises adding fractions with exercises that never repeat and instant marking.
Start the exercises →Frequently asked questions
How do you add two fractions with the same denominator?
You simply add the numerators together, and keep the same denominator. For example 2/5 + 1/5 = 3/5: the denominators (5) don't change, only the numerators (2 and 1) are added.
Why doesn't the denominator change when adding?
The denominator shows the size of the parts (how many pieces the whole was cut into). Adding fractions with the same denominator means adding parts that are the same size — so the size of the parts doesn't change, only how many of them there are.
What if the result is more than the denominator?
If the numerator you get is equal to or bigger than the denominator, the result is more than 1 whole. For example 3/4 + 2/4 = 5/4, which represents 1 whole plus 1/4 (you have more parts than the whole originally contained).