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Complex Fractions



Key Terms
What Is a Complex Fraction
Simplifying — Method 1: Division
Simplifying — Method 2: LCD
Complex Fractions with Sums or Differences
Complex Fractions with Mixed Numbers
Nested Complex Fractions
Common Mistakes
Complex Fractions at a Glance



Simplifying Stacked Expressions

A complex fraction contains fractions within its numerator, denominator, or both. Expressions like 1234\frac{\frac{1}{2}}{\frac{3}{4}} or 23+15\frac{\frac{2}{3} + 1}{5} are complex fractions. Two primary methods simplify them: treating the main fraction bar as division, or multiplying by the least common denominator of all internal fractions.

Key Terms

Complex Fraction— the central concept on this page
Reciprocal— used to simplify complex fractions via the division method
Common Denominator— the LCD method clears internal denominators in one step

See All Arithmetic Definitions →


What Is a Complex Fraction

A complex fraction has a fraction in its numerator, its denominator, or both. The main fraction bar separates the overall numerator from the overall denominator, while smaller fraction bars appear within.

Examples include:

1234253456\frac{\frac{1}{2}}{3} \quad \frac{4}{\frac{2}{5}} \quad \frac{\frac{3}{4}}{\frac{5}{6}}


The first has a fraction only in the numerator. The second has a fraction only in the denominator. The third has fractions in both positions.

Complex fractions arise naturally in algebra, physics, and rate problems. Any division of fractions can be written as a complex fraction: 23÷45\frac{2}{3} \div \frac{4}{5} equals 2345\frac{\frac{2}{3}}{\frac{4}{5}}.

Simplifying — Method 1: Division

The main fraction bar represents division. A complex fraction abcd\frac{\frac{a}{b}}{\frac{c}{d}} means ab÷cd\frac{a}{b} \div \frac{c}{d}.

Apply the rule for dividing fractions: multiply by the reciprocal.

3456=34÷56=34×65=1820=910\frac{\frac{3}{4}}{\frac{5}{6}} = \frac{3}{4} \div \frac{5}{6} = \frac{3}{4} \times \frac{6}{5} = \frac{18}{20} = \frac{9}{10}


When only the numerator or only the denominator contains a fraction, the same approach works. For 234\frac{\frac{2}{3}}{4}, rewrite 4 as 41\frac{4}{1} and proceed: 23÷41=23×14=212=16\frac{2}{3} \div \frac{4}{1} = \frac{2}{3} \times \frac{1}{4} = \frac{2}{12} = \frac{1}{6}.

Simplifying — Method 2: LCD

Multiplying the entire complex fraction by a form of 1 clears internal denominators. Find the LCD of all denominators appearing anywhere in the complex fraction, then multiply both the overall numerator and overall denominator by this LCD.

For 1234\frac{\frac{1}{2}}{\frac{3}{4}}, the internal denominators are 2 and 4. The LCD is 4.

1234×44=12×434×4=23\frac{\frac{1}{2}}{\frac{3}{4}} \times \frac{4}{4} = \frac{\frac{1}{2} \times 4}{\frac{3}{4} \times 4} = \frac{2}{3}


This method is especially efficient when the numerator or denominator contains sums or differences of fractions, avoiding multiple division steps.
Method Procedure Example Best when
Division rewrite the main fraction bar as ÷, then multiply the top by the reciprocal of the bottom (3⁄4) ⁄ (5⁄6) = (3⁄4)(6⁄5) = 9⁄10 numerator and denominator are each a single fraction
LCD multiply both the overall numerator and overall denominator by the LCD of every internal denominator (1⁄2) ⁄ (3⁄4) × (4⁄4) = 2 ⁄ 3 numerator or denominator contains sums or differences of fractions

Complex Fractions with Sums or Differences

When the numerator or denominator of a complex fraction contains addition or subtraction, simplify that part first using adding and subtracting fractions rules, then proceed with either method.

Simplify 12+1314\frac{\frac{1}{2} + \frac{1}{3}}{\frac{1}{4}}:

First, combine the numerator: 12+13=36+26=56\frac{1}{2} + \frac{1}{3} = \frac{3}{6} + \frac{2}{6} = \frac{5}{6}.

The complex fraction becomes 5614=56×41=206=103\frac{\frac{5}{6}}{\frac{1}{4}} = \frac{5}{6} \times \frac{4}{1} = \frac{20}{6} = \frac{10}{3}.

Alternatively, multiply by the LCD of 2, 3, and 4, which is 12. Both approaches reach the same answer.

Complex Fractions with Mixed Numbers

When a complex fraction contains mixed numbers, convert them to improper fractions before simplifying.

Simplify 212114\frac{2\frac{1}{2}}{1\frac{1}{4}}:

Convert: 212=522\frac{1}{2} = \frac{5}{2} and 114=541\frac{1}{4} = \frac{5}{4}.

5254=52×45=2010=2\frac{\frac{5}{2}}{\frac{5}{4}} = \frac{5}{2} \times \frac{4}{5} = \frac{20}{10} = 2


The 5s cancel during multiplication, leaving 42=2\frac{4}{2} = 2 directly.

Nested Complex Fractions

Occasionally, a complex fraction appears within another complex fraction. Simplify from the innermost fraction outward.

Simplify 1112\frac{1}{\frac{1}{\frac{1}{2}}}:

Start with the innermost: 112=1×21=2\frac{1}{\frac{1}{2}} = 1 \times \frac{2}{1} = 2.

Substitute back: 12\frac{1}{2}.

Most practical problems involve at most one level of nesting. The strategy remains the same regardless of depth: resolve the innermost structure first, then work outward until only a simple fraction remains.

Common Mistakes

Forgetting to flip when dividing is a frequent error. The complex fraction 2345\frac{\frac{2}{3}}{\frac{4}{5}} requires multiplying by 54\frac{5}{4}, not 45\frac{4}{5}.

Applying the LCD incorrectly causes problems. The LCD must multiply the entire numerator and the entire denominator, not just parts of them.

Leaving answers unsimplified wastes effort. After clearing the complex structure, check whether the result reduces to simplest form.

Mixing up which fraction to flip leads to inverted answers. In ab÷cd\frac{a}{b} \div \frac{c}{d}, only the divisor cd\frac{c}{d} gets flipped, never the dividend ab\frac{a}{b}.

Complex Fractions at a Glance

The page covered what a complex fraction is, two simplification methods (division and LCD), the special cases with sums, mixed numbers, or nesting, and the common pitfalls. The table below collects every situation encountered with the move to make and a worked example.
Situation What to do Example
Definition a fraction with a fraction in its numerator, denominator, or both (3⁄4) ⁄ (5⁄6)
Main bar = division the overall fraction bar represents division of top by bottom (a⁄b) ⁄ (c⁄d) = (a⁄b) ÷ (c⁄d)
Fraction over fraction keep, change, flip — multiply top by reciprocal of bottom (3⁄4) ⁄ (5⁄6) = (3⁄4)(6⁄5) = 9⁄10
Fraction over whole write the whole as whole⁄1, then proceed (2⁄3) ⁄ 4 = (2⁄3)(1⁄4) = 1⁄6
Whole over fraction multiply the whole by the reciprocal of the fraction 4 ⁄ (2⁄5) = 4 × (5⁄2) = 10
Sums or differences inside combine that part first (or use the LCD method), then simplify the resulting complex fraction (1⁄2 + 1⁄3) ⁄ (1⁄4) → (5⁄6) ⁄ (1⁄4) = 10⁄3
Mixed numbers inside convert every mixed number to an improper fraction first (2 1⁄2) ⁄ (1 1⁄4) = (5⁄2)(4⁄5) = 2
Nested complex fraction resolve the innermost fraction first, then work outward 1 ⁄ (1 ⁄ (1⁄2)) → 1 ⁄ 2
Only the divisor flips in a⁄b ÷ c⁄d, the dividend a⁄b stays put — never flip it (2⁄3) ⁄ (4⁄5) needs ×(5⁄4), not ×(4⁄5)
Reduce the final result after clearing the complex structure, check whether the answer simplifies to lowest terms 18⁄20 → 9⁄10