Fraction Calculator guide
How to Subtract Fractions with Unlike Denominators
To subtract fractions, find a common denominator, rewrite both fractions over it, then subtract the numerators and keep the denominator. For 3/4 − 1/6, the common denominator is 12, giving 9/12 − 2/12 = 7/12.
It is the same method as adding
Everything from the addition guide applies here unchanged. Find a common denominator, rewrite both fractions, then work on the numerators only.
The single difference is the operation in the middle. If you can add fractions, you can subtract them.
A worked example
Take 3/4 − 1/6.
The denominators are 4 and 6. The smallest number both divide into is 12.
3/4 becomes 9/12, because 4 × 3 = 12 so the top is multiplied by 3 too.
1/6 becomes 2/12, because 6 × 2 = 12 so the top is multiplied by 2.
Now subtract the numerators: 9 − 2 = 7. The answer is 7/12, which cannot be simplified.
The order matters
Unlike addition, subtraction is not reversible. 3/4 − 1/6 is 7/12, but 1/6 − 3/4 is −7/12.
Keep the fractions in the order the question gives them. When you are juggling common denominators it is surprisingly easy to swap them without noticing.
A negative answer is perfectly valid, and worth double-checking rather than assuming you made an error. If you subtracted a bigger fraction from a smaller one, negative is correct.
Subtracting mixed numbers, and borrowing
This is where subtraction gets genuinely harder than addition, and it is worth going slowly.
Take 3¼ − 1⅔. Subtracting the whole numbers gives 2. But the fractions give ¼ − ⅔, which is negative — you cannot take two thirds from one quarter.
The fix is borrowing, exactly as in ordinary column subtraction. Take 1 from the whole number and add it to the fraction as a full unit.
3¼ becomes 2 and 1¼, which is 2 and 5/4. Now: 2 − 1 = 1 for the whole numbers, and 5/4 − ⅔. With a denominator of 12 that is 15/12 − 8/12 = 7/12. So the answer is 1 7/12.
The alternative that avoids borrowing
If borrowing feels error-prone, convert both mixed numbers to improper fractions first and skip it entirely.
3¼ is 13/4 and 1⅔ is 5/3. Over a denominator of 12: 39/12 − 20/12 = 19/12. Converting back gives 1 7/12 — the same answer.
The numbers are larger this way, but there is no borrowing step to get wrong. For anything more complicated than a single subtraction, this route tends to be more reliable.
