Subtracting Fractions Calculator — With Step-by-Step Working
Enter the numerators and denominators of two fractions and the calculator finds the least common denominator, converts both fractions, subtracts the numerators, and simplifies the result — showing every step so you can follow the working.
Find the least common denominator of 4 and 3
Convert 3/4 to denominator 12
Convert 1/3 to denominator 12
Subtract the numerators
Simplify (divide numerator and denominator by their GCD)
- 1
Least common denominator (LCD)
LCM(4, 3) = 12 - 2
Convert first fraction to LCD
3 × (12 ÷ 4) = 9 ÷ 12 - 3
Convert second fraction to LCD
1 × (12 ÷ 3) = 4 ÷ 12 - 4
Subtract numerators, then simplify
(9 − 4) ÷ 12 = 5/12 = 0.416667
How does this calculator work?
To subtract a/b − c/d: find LCD = LCM(b,d); convert to LCD·(a/b) − LCD·(c/d), all over LCD; subtract numerators; simplify by GCD. Example: 3/4 − 1/3 = 9/12 − 4/12 = 5/12.
Formula
How this is calculated
You can only subtract fractions that share the same denominator. When denominators differ, the first step is to find the least common denominator (LCD) — the smallest positive integer that both denominators divide into evenly. The LCD equals |d₁ × d₂| / GCD(d₁, d₂) (the product of the two denominators divided by their greatest common divisor).
Once you have the LCD, convert each fraction by multiplying numerator and denominator by the factor needed to reach the LCD: a/b becomes a·(LCD/b) / LCD. Now both fractions share the same denominator and you can subtract numerators directly. The resulting fraction is then simplified by dividing both numerator and denominator by their GCD.
The method works for any integers — positive, negative, or one (a fraction equal to a whole number). If the result numerator is 0 the fractions are equal; if the numerator is negative the result is a negative fraction. Mixed numbers (like 1½) should be converted to improper fractions (3/2) before entering.
Frequently asked questions
Fractions represent parts of a whole divided into equal slices. Before you can subtract, the slices must be the same size — which means the denominators must match. The LCD gives the finest common denominator that avoids unnecessary large numbers.
An improper fraction like 7/4 is mathematically correct. You can convert it to a mixed number (1¾) by dividing: 7 ÷ 4 = 1 remainder 3, so the mixed number is 1 and 3/4. The calculator shows the result as an improper fraction in lowest terms.
Convert the whole number to a fraction by writing it over 1 — for example 3 = 3/1. Then use this calculator with denominator = 1 for that number. The LCD will equal the other fraction's denominator, and the conversion is straightforward.
Also known as
TG we-Calculate Editorial Team. (2026). Subtracting Fractions Calculator — With Step-by-Step Working [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/subtracting-fractions-calculator
TG we-Calculate Editorial Team. "Subtracting Fractions Calculator — With Step-by-Step Working." TG we-Calculate. 2026. https://we-calculate.com/calculator/subtracting-fractions-calculator.
TG we-Calculate Editorial Team, "Subtracting Fractions Calculator — With Step-by-Step Working," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/subtracting-fractions-calculator
@misc{wecalculate_subtracting_fractions_calculator, title = {Subtracting Fractions Calculator — With Step-by-Step Working}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/subtracting-fractions-calculator}}, year = {2026}, note = {TG we-Calculate} }
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