Gunning Fog index calculator

The formula

Gunning Fog = 0.4 × ((words / sentences) + 100 × (complex_words / words))

“Complex words” means 3+ syllable words, excluding proper nouns, common compounds (like “butterfly”), and words made complex only by inflectional endings (“-es,” “-ed,” “-ing”).

The output approximates years of formal education needed. A score of 12 means “requires a high-school education to read on first pass.” A score of 17 means “requires four years of college.”

Score interpretation

• 6:6th grade. Easy reading. Comic books, children’s magazines.
• 8:Plain English. Reader’s Digest. The SEC’s recommended target for investor communications.
• 10: Time magazine. Easy reading for adults.
• 12: High school. Most business and consumer writing.
• 14: Two-year college. Wall Street Journal, Harvard Business Review.
• 16: Four-year college. Academic writing.
• 17+: Graduate level. Specialist publications.

Where Gunning Fog matters

• SEC filings & prospectuses— the SEC has flagged unnecessarily complex prospectus language; Gunning Fog of 8–10 is the unofficial target.
• Annual reports— the Berkshire Hathaway annual letter (famously clear) scores around 9–10. Most Fortune 500 reports score 15+.
• Customer-facing financial copy— insurance policies, loan agreements, and bank disclosures benefit from Gunning Fog ≤ 10.
• Business journalism— bloggers and business writers often check Gunning Fog as a sanity check against jargon.

Reducing the fog

The formula has two levers: sentence length and complex-word fraction. To lower your score:

• Cap sentences at 20 words. Most over-25 sentences hide a second sentence trying to escape.
• Audit polysyllabic words.“Utilize” → “use.” “Implementation” → “use” (in many contexts). “Communicate” → “tell.”
• Avoid nominalizations.“Made a decision” → “decided.” “Gave consideration to” → “considered.”
• Cut wind-up phrases.“It should be noted that” — just say it.