What is the four-fifths (80%) rule?

Under the Uniform Guidelines on Employee Selection Procedures (29 C.F.R. § 1607.4(D)), a selection rate for any race, sex, or ethnic group which is less than four-fifths (80%) of the rate for the group with the highest selection rate is generally regarded by Federal enforcement agencies as evidence of adverse impact.

How is the four-fifths rule different from statistical significance?

The four-fifths rule compares the sizes of selection rates (a practical-significance screen), while a statistical test such as the two-proportion z-test asks whether the observed difference is larger than chance would produce. They are complementary questions and can disagree, especially in small or very large samples.

What about small samples?

The regulation itself cautions that differences based on numbers too small to be reliable may not constitute adverse impact, and that evidence over a longer period may be considered. Statistically, the z-test's normal approximation is questionable when expected counts are below about 5 per cell.

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Four-fifths (80%) rule calculator

Q: Is the 80% threshold legally binding?

No. The regulation frames it as a general rule of thumb used by enforcement agencies, not a bright-line legal test. Smaller differences can still constitute adverse impact when statistically and practically significant, and larger differences may not when based on small, non-significant numbers.

Enter applicants evaluated and selected for two or more groups to get selection rates, impact ratios against the highest-rate group, adverse impact flags at the 4/5ths (0.80) threshold, the additional selections needed to comply, and a two-proportion z-test of each difference. No account, nothing stored — results are computed on the server and returned on this page.

Calculator

The form is prefilled with an illustrative example (not data from any real selection process) so you can see how results look. Replace the numbers with your own and press Compute.

Group	Applicants evaluated	Number selected

Leave unused rows blank. At least two groups are required.

Results

Illustrative example — these numbers are placeholder inputs, not observations from a real battery. Every figure below is computed live by the same engine that scores your own entries.

Reference group (highest selection rate): Group A. Each other group's impact ratio is its selection rate divided by the reference group's rate; a ratio below 0.80 is flagged per the four-fifths rule.

Group	Evaluated	Selected	Selection rate	Impact ratio	4/5ths result	Additional selections to comply	z	p (two-sided)
Group A	60	42	70.0%	—	Reference	—	—	—
Group B	55	28	50.9%	0.727	Below 4/5ths	3	-2.10	0.036

At least one group falls below four-fifths of the reference group's selection rate. The “additional selections to comply” column shows the smallest number of extra selections from that group (with the same applicant pool) that would raise its ratio to at least 0.80. This is an arithmetic statement about the counts entered, not hiring advice.

The z and p columns report a pooled two-proportion z-test of each group's selection rate against the reference group's. The four-fifths rule is a rule of thumb about the size of the disparity; statistical significance asks a separate, complementary question — whether the difference is larger than chance alone would plausibly produce. The two can disagree: small samples can fail to reach significance despite a large ratio gap, and very large samples can be statistically significant with a ratio well above 0.80.

Monitoring adverse impact across a real hiring process?

This calculator handles one snapshot of counts. AxisPoint, the workplace assessment product on this platform, ties the same four-fifths analysis to candidate batteries: group tagging from the console, a cutoff-score simulator, and UGESP compliance reporting per battery. Employer access is arranged after an inquiry — use the request form below.

See AxisPoint

What the regulation says

The four-fifths rule comes from the Uniform Guidelines on Employee Selection Procedures. The operative sentence, quoted verbatim from 29 C.F.R. § 1607.4(D):

“A selection rate for any race, sex, or ethnic group which is less than four-fifths (⁴⁄₅) (or eighty percent) of the rate for the group with the highest rate will generally be regarded by the Federal enforcement agencies as evidence of adverse impact, while a greater than four-fifths rate will generally not be regarded by Federal enforcement agencies as evidence of adverse impact.”

The same paragraph immediately qualifies the threshold in both directions: smaller differences “may nevertheless constitute adverse impact, where they are significant in both statistical and practical terms,” and greater differences “may not constitute adverse impact where the differences are based on small numbers and are not statistically significant.” That is why this calculator pairs the ratio with a significance test rather than treating 0.80 as a verdict.

Source: 29 C.F.R. § 1607.4(D), Uniform Guidelines on Employee Selection Procedures (eCFR). The formula: impact ratio = (selection rate of a group) ÷ (selection rate of the highest-rate group); a ratio below 0.80 is flagged.

Frequently asked questions

What is the four-fifths rule?

A screening convention from the Uniform Guidelines (29 C.F.R. § 1607.4(D)): compare each group's selection rate to the highest group's rate. When the ratio falls below four-fifths (80%), Federal enforcement agencies will generally regard that as evidence of adverse impact for the selection procedure being examined.

Is the 80% threshold legally binding?

No — it is an enforcement rule of thumb, not a statute or a bright-line legal test. The regulation says agencies will “generally” treat sub-0.80 ratios as evidence of adverse impact, and explicitly contemplates exceptions in both directions. Courts and agencies also look at statistical significance, practical significance, and the reliability of the underlying numbers.

How is the 4/5ths rule different from statistical significance?

The impact ratio measures the size of the disparity between selection rates. A statistical test — here, the pooled two-proportion z-test — asks how likely a difference at least this large would be if selection were unrelated to group membership. They answer different questions: a large ratio gap in a tiny sample may be pure chance, and a trivial gap in a huge sample can be statistically significant.

What are the limits with small samples?

Two kinds. Legally, the regulation cautions that differences “based on small numbers” that are not statistically significant may not constitute adverse impact, and that impact evidence over a longer period may be considered. Statistically, the z-test's normal approximation becomes unreliable when an expected count (group size × pooled rate, or its complement) falls below about 5 — the calculator marks such comparisons with †.

Does this calculator store my data?

No. The counts you enter are used to compute the page you get back and are not saved, logged to any dataset, or associated with you. The one exception is explicit: if you purchase the compliance PDF, the counts covered by that purchase are saved with it so the report can be regenerated for you later.

What the toolset provides

Group tagging — label each candidate as Group A, Group B, or Untagged directly from your battery console.
Cutoff-score simulator — choose any facet or domain column and a pass-mark threshold; the platform instantly computes the 4/5ths ratio, flags potential adverse impact, and estimates the additional hires needed to comply.
UGESP compliance PDF — a downloadable report containing the adverse impact table, per-instrument reliability and validity evidence from published sources, and a Selection Procedure Documentation section formatted for UGESP record-keeping.

Access is gated per battery by a manual enablement step after an inquiry, so the tooling is visible to your HR team only when it is relevant to a specific hiring process.

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To enable the adverse impact toolset for your organisation, send a brief note below. Include your battery name or role if you have one in mind.

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