# Subtracting Fractions Calculator

URL: https://speedycalculator.com/calculators/math/subtracting-fractions/
Last updated: 2026-10-30

> The subtracting fractions calculator subtracts one fraction or mixed number from another using the least common denominator and gives a simplified fraction, mixed number and decimal with steps.

## Inputs

- My fractions are in
- Fraction 1: whole
- Fraction 1: numerator
- Fraction 1: denominator
- Fraction 2: whole
- Fraction 2: numerator
- Fraction 2: denominator

## Results

- Difference
- Mixed number
- Decimal
- Steps

## Formula

```
a/b − c/d = (a·(L/b) − c·(L/d)) / L,  L = LCM(b, d)
```

## Explanation

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.

## 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.

## FAQ

**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.


## Sources

- [OpenStax – Prealgebra 2e](https://openstax.org/details/books/prealgebra-2e)
- [Wolfram MathWorld – Fraction](https://mathworld.wolfram.com/Fraction.html)