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Text Complexity Score Calculator

Work out text complexity score instantly with clear inputs, formula shown and shareable results.

About Text Complexity Score Calculator

The Gunning Fog index is 0.4 times the sum of average sentence length and the percentage of complex words, giving the years of education a reader needs. Twenty-two word sentences with 18% complex words scores 16 - undergraduate level. Adding a passive voice penalty produces a composite that captures a further real barrier to comprehension.

Formulas

Gunning Fog index

0.4 x (average sentence length + percent complex words)

Composite

fog x 4 plus a passive voice penalty, capped at 100

Worked example

With the default values below, Text Complexity Score Calculator returns Gunning Fog Index of 16.00. Change any input above and every figure here is recalculated in your browser.

Inputs used

Average sentence lengthminimum 1 words
22 words
Words of three or more syllablesaccepts 0–100 %
18 %
Sentences in the passive voiceaccepts 0–100 %
25 %

Results

Gunning Fog Index
16.00
Composite Complexity Score
74.0 /100
Years Of Education Implied
16.0
Reading Level
Undergraduate level

Step by step

  1. 1Values used
  2. 2Gunning Fog index
  3. 3Composite
  4. 4Gunning Fog Index= 16.00
  5. 5Composite Complexity Score= 74.0 /100
  6. 6Years Of Education Implied= 16.0
  7. 7Reading Level= Undergraduate level

Assumptions and limits

  • The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Why does the passive voice matter?

Because it hides the actor and adds words, increasing processing load. Plain language guidance targets under 10% passive constructions.

Which readability index is best?

They correlate strongly. Fog and Flesch-Kincaid are the most cited; use one consistently rather than comparing across formulas.

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