Dale-Chall Readability Formula: How It Differs From Flesch-Kincaid (And When to Use Each)

If you’ve already run a Flesch-Kincaid check on a piece of content, you might assume your readability homework is done. It isn’t. Flesch-Kincaid and the Dale-Chall Readability Formula measure two genuinely different things, and they can land several grade levels apart on the exact same paragraph. Flesch-Kincaid judges difficulty by sentence length and syllables per word. Dale-Chall asks a more direct question: are the words themselves familiar to an average reader? For content aimed at kids, patients, non-native speakers, or the general public, that distinction decides which score you should actually trust.

Quick answer: Flesch-Kincaid scores text by sentence length and syllables per word, producing a U.S. grade level. Dale-Chall scores text by checking each word against a list of roughly 3,000 terms familiar to fourth graders, then factors in sentence length. Use Flesch-Kincaid for general web and marketing copy; use Dale-Chall for children’s material, plain-language writing, and anything meant for low-literacy audiences.

What Makes Dale-Chall Different From Flesch-Kincaid

Flesch-Kincaid runs on two inputs — average sentence length and average syllables per word — and assumes that longer words and longer sentences are automatically harder to process. That assumption holds up often enough to be useful, but syllable count is only a proxy for difficulty. It isn’t difficulty itself.

Dale-Chall skips the proxy and checks vocabulary directly. Edgar Dale and Jeanne Chall built the formula in 1948 by comparing every word in a passage against a curated list of roughly 3,000 words that at least 80% of American fourth graders recognized. Anything not on that list counts as “difficult,” regardless of how many syllables it has. The formula then blends that percentage with sentence length:

Raw score = 0.1579 × (percentage of difficult words) + 0.0496 × (average sentence length)

If difficult words make up more than 5% of the text, add a flat 3.6365 to the result. That single adjustment explains why a passage with short, tidy sentences can still land in a harder reading band than you’d expect — vocabulary is dragging the score up, not sentence structure.

Here’s what that looks like with real numbers. Say you’re checking a 150-word passage split into 12 sentences, and 18 of those words don’t appear on the Dale-Chall list:

• Percentage of difficult words (PDW) = (18 ÷ 150) × 100 = 12%
• Average sentence length (ASL) = 150 ÷ 12 = 12.5
• Raw score = (0.1579 × 12) + (0.0496 × 12.5) = 1.89 + 0.62 = 2.51
• Since PDW is above 5%, add 3.6365 → final score ≈ 6.15, roughly a 6th-to-9th-grade band

Run that same 150-word passage through Flesch-Kincaid and, if the sentences are short, it might score a full grade or two easier — because Flesch-Kincaid never checks whether those 18 unfamiliar words are actually common ones. That’s the entire disagreement in a nutshell: compare “The vet gave the dog a shot” with “The clinician administered an injection.” Both are short, plain sentences by syllable-and-length standards. Only one of them uses words a general reader will recognize on sight.

When Dale-Chall Is the Better Fit

Dale-Chall earns its keep whenever unfamiliar vocabulary — not sentence complexity — is the real barrier to comprehension:

• Children’s books and early-reader content, where publishers need vocabulary matched to a child’s developing word bank, not just short sentences.
• Plain-language government and legal notices — benefits letters, voting materials, public health guidance — where regulations often specify a target reading level.
• Adult literacy and ESL materials, where readers may have solid comprehension skills but a smaller working vocabulary.
• Patient education handouts, usually paired with the SMOG Index, since both formulas were designed with lower-literacy audiences in mind.

One real limitation to flag before you lean on it: Dale-Chall’s original word list dates to 1948 and was last substantially revised in 1995. Depending on the tool, it can still flag everyday modern words — “email,” “app,” “website” — as unfamiliar simply because they postdate the list. A few readability sites pushed out refreshed word lists in 2025 to correct for this gap, so before you trust a Dale-Chall score on anything with contemporary or tech-related vocabulary, check which word list the calculator is actually running against.

When Flesch-Kincaid Is the Better Fit

For most everyday content — blog posts, landing pages, marketing copy, help documentation — Flesch-Kincaid is the more practical default. It’s already built into Microsoft Word and most SEO and editing tools, so teams end up using it without installing anything new. A grade-level number is also easier to explain to a client or editor who’s never heard of a word-familiarity list — “aim for grade 8” needs no further context. And because it scores purely on sentence and word length rather than checking words against a fixed list, it doesn’t choke on new terminology, brand names, or industry jargon the way an outdated word list can.

The trade-off runs in the opposite direction from Dale-Chall’s weakness: Flesch-Kincaid can underrate genuinely hard vocabulary if the sentences carrying it stay short. Write “utilize synergistic frameworks” in a five-word sentence and Flesch-Kincaid will still call it easy, because it never asked whether readers actually know those words.

If you’ve already got a dedicated post on the Flesch-Kincaid Grade Level formula, this is a natural spot to link to it — readers who found this page already checked their Flesch-Kincaid score and want the next layer of nuance.

Score Interpretation Side-by-Side

The two formulas don’t share a scale, so a “6” doesn’t mean the same thing in both systems. Here’s roughly how the grade bands line up:

Dale-Chall Score	Approximate Grade Band	Flesch-Kincaid Grade Level	Reading Experience
4.9 or below	Pre-K – 4th grade	0 – 4	Very easy; picture books, early readers
5.0 – 5.9	4th – 6th grade	5 – 6	Easy; conversational, consumer-facing
6.0 – 6.9	6th – 9th grade	7 – 8	Fairly easy; most blog and news content
7.0 – 7.9	9th – 10th grade	9 – 10	Standard plain English
8.0 – 8.9	10th – 12th grade	11 – 12	Fairly difficult; some academic content
9.0 – 9.9	12th grade – college	13 – 14	Difficult; specialist or professional audiences
10.0 and above	College graduate	15+	Very difficult; academic or legal writing

Treat this as a rough alignment, not a conversion chart. The two formulas weigh different signals, so a text with unusual vocabulary relative to its sentence length can land in different rows for each score. For general web content, a Flesch-Kincaid grade of 7–9 paired with a Dale-Chall score of 6.0–7.9 is a reasonable target for most audiences.

How to Check Both Scores on the Same Text

Running both formulas on the same draft takes a few extra minutes and gives you a far more honest picture than either score alone:

1. Clean the text first. Strip headers, bullet points, and captions before scoring flowing prose — list fragments skew average sentence length in both formulas.
2. Run both checks, either separately or through a combined readability tool that outputs both at once.
3. Compare the results. If Flesch-Kincaid comes back easy but Dale-Chall comes back harder, the problem is almost certainly vocabulary — look for specialized terms or formal phrasing a general reader wouldn’t recognize on sight.
4. If both scores come back hard, treat it as two problems, not one. Long sentences carrying unfamiliar words compound each other, so shorten sentences and simplify word choice together, then retest.

A handful of word swaps — “start” instead of “commence,” “use” instead of “utilize” — can shift a Dale-Chall score noticeably without touching your sentence structure at all. And because scores can vary between calculators even for the same formula, depending on how each tool handles abbreviations and punctuation, don’t chase an exact number. Chase agreement between the two scores, then read the piece aloud as a final check.

The Bottom Line

Flesch-Kincaid and Dale-Chall aren’t competing for the same job. Flesch-Kincaid tells you whether your sentence construction is doing readers any favors; Dale-Chall tells you whether your word choices are. For most general web content, Flesch-Kincaid is the right first check. The moment your audience includes children, low-literacy adults, non-native speakers, or anyone reading plain-language-mandated material, run Dale-Chall alongside it. Used together, the two formulas catch problems that either one would miss on its own.

Related posts:

Passive Voice Readability Score: What Actually Moves It

The UX Writing Readability Checklist for Product Copy

Plain Language Writing Guide: How to Write Clearly for Every Reader