FractionReference

Subtract fractions

Two values in, one exact difference out — negative answers included, stated plainly.

Try: — fractions, mixed numbers and decimals all work, negatives included.

Common questions

How do I subtract fractions with different denominators?
Rewrite both over a common denominator, then subtract the numerators. For 3/8 − 1/4: 1/4 = 2/8, and 3/8 − 2/8 = 1/8.
What if the answer is negative?
1/4 − 3/8 = −1/8, and the page says so. A negative fraction is a number like any other; the sign is carried on the numerator throughout.
How do I subtract a mixed number?
Type it as written — 2 1/4 − 7/8 works. Mixed numbers become improper fractions internally, so there is no borrowing to get wrong.
Where this comes from. Exact rational arithmetic on the values shown — fractions are pairs of integers until display, and inch–metric conversion uses 25.4 mm to the inch, exact by definition since 1959. See the full methodology.