What is an LCD?
The least common denominator is the smallest shared denominator for two or more fractions.
LCD Calculator
Find the least common denominator of two fractions so you can add or subtract them easily.
Enter two fractions
Provide both numerators and denominators to compute the LCD and rewritten equivalents.
About this calculator
How to use LCD Calculator, plus the formulas and logic behind the results.
Tool description
The least common denominator is the least common multiple of the denominators. This tool also rewrites both fractions with that shared denominator.
How to use
- Enter the first fraction’s numerator and denominator.
- Enter the second fraction’s numerator and denominator.
- Select Calculate to find the LCD.
- Use the rewritten fractions when adding or subtracting.
Formulas & reference
LCD = LCM(d1, d2) = |d1 × d2| ÷ gcd(d1, d2)Equivalent: n/d = (n × LCD/d) / LCD
LCD tips
- LCD of 1/6 and 1/8 is 24
- 1/6 = 4/24 and 1/8 = 3/24
- Use LCD before adding or subtracting
- Any common multiple works; LCD is the smallest
Calculation logic
The LCM of the two denominators is computed from their GCD. Each numerator is scaled by LCD ÷ original denominator.
LCD is the same idea as LCM when you only care about denominators.
LCD Calculator FAQ
Common questions about this calculator and how to use the results.
Is LCD the same as LCM?
For denominators, yes—the LCD is the LCM of those denominators.
Why rewrite fractions with the LCD?
Equal denominators let you add or subtract numerators directly.
What if denominators are equal?
The LCD is that denominator, and the fractions stay unchanged.
Can numerators be zero?
Yes. Zero fractions still have a denominator and an LCD with another fraction.
Does order matter?
No. LCM(d1, d2) equals LCM(d2, d1).