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Subtracting fractions with the same denominator follows the same logic as adding them: the denominator names the unit, so subtract the numerators and keep the denominator. 5/8 - 2/8 = 3/8, just as 5 eighths minus 2 eighths equals 3 eighths. This extends to subtracting from mixed numbers when regrouping is not needed (2 3/4 - 1 1/4 = 1 2/4 = 1 1/2). Subtraction of fractions models real situations like "how much is left?" or "what is the difference?"
Use fraction strips: start with a shaded amount and remove parts. Connect to the number line by showing the distance between two fractions. Practice word problems involving remaining portions or differences.
You already know how to add fractions with the same denominator — you add the numerators and keep the denominator unchanged, because the denominator names the unit and units don't change when you combine or remove them. Subtraction follows the same rule. If you have 5/8 and remove 2/8, you are removing 2 eighth-pieces from a collection of 5 eighth-pieces, leaving 3 eighth-pieces: 5/8 − 2/8 = 3/8.
The key is thinking of the denominator as a unit name, not a number to operate on. "Eighths" is a unit, like "apples." If you have 5 apples and take away 2 apples, you have 3 apples — you never change the word "apples." Fractions work the same way: 5 eighths minus 2 eighths equals 3 eighths. The denominator stays 8 because the size of each piece has not changed; you just have fewer of them.
This means the denominator is only unchanged when the two fractions share the same denominator — when they are measured in the same unit. You cannot directly subtract 5/8 − 1/3 using this rule because the pieces are different sizes. That problem requires converting to like denominators first, which comes later. For now, same-denominator subtraction is the clean, simple case, and mastering it builds the intuition you will need.
For mixed numbers like 2 3/4 − 1 1/4, handle the whole-number parts and fraction parts separately. Subtract the fractions: 3/4 − 1/4 = 2/4. Subtract the whole numbers: 2 − 1 = 1. The result is 1 2/4, which simplifies to 1 1/2. This works as long as the fraction you are subtracting is not larger than the fraction you are subtracting from — the regrouping case, where you need to borrow from the whole number, is a harder step addressed later.