Subtracting fractions needs a common denominator, just like adding. With mixed numbers it is usually easiest to convert to improper fractions first, which avoids borrowing.
How to use the Subtracting Fractions Calculator
- My fractions are in
- Fraction 1: whole
- Fraction 1: numerator
- Fraction 1: denominator
- Fraction 2: whole
- Fraction 2: numerator
- Fraction 2: denominator
Everything is calculated in your browser, so results appear instantly and nothing you type is sent to a server.
How it works
The calculator converts mixed numbers to improper fractions, rewrites both fractions over the least common denominator, subtracts the numerators and simplifies.
Formula
a/b − c/d = (a·(L/b) − c·(L/d)) / L, L = LCM(b, d)
Worked example
Inputs — My fractions are in: Simple fraction; Fraction 1: numerator: 3; Fraction 1: denominator: 4; Fraction 2: numerator: 2; Fraction 2: denominator: 5.
Results — Difference = 7/20; Mixed number = 7/20; Decimal = 0.35; Steps = 1. Least common denominator: LCD(4, 5) = 20
2. Rewrite: 3/4 = 15/20, 2/5 = 8/20
3. Subtract the numerators: 15 − (8) = 7, giving 7/20
4. Simplify: 7/20.
Key terms
- Common denominator
- A shared denominator that allows fractions to be combined.
Frequently asked questions
What is 3/4 − 2/5?
15/20 − 8/20 = 7/20.
How do I subtract mixed numbers?
Convert to improper fractions, subtract, convert back.
What if the answer is negative?
That is fine: 1/4 − 1/2 = −1/4.
Do I always need the least common denominator?
No, any common denominator works, but the LCD keeps numbers small.