Definition

The four-fifths rule is a federal screening test for adverse impact in hiring and promotion. If one race, sex or ethnic group is selected at less than 80 percent of the rate of the group selected most often, federal agencies generally treat the gap as evidence of adverse impact.

Also known as: 80 percent rule, 80% rule, 4/5ths rule

Key figures

United States (federal)As of Oct 13, 2026

Adverse-impact threshold
Below 80% of the highest group’s rate29 CFR 1607.4(D)
Simplified records
Employers with 100 or fewer employees29 CFR 1607.15(A)(1)
How often to check selection rates
At least once a year29 CFR 1607.15(A)(2)(a)
Groups to analyze
2% or more of the labor area or workforce29 CFR 1607.15(A)(2)(a)

How it works

Start with the selection rate of each group: the number hired or promoted divided by the number who applied. Find the highest rate. Divide every other group's rate by it. A result under 0.80 is the signal federal agencies generally read as adverse impact; a result above it generally is not.

The rule is a rule of thumb, not a legal finding. Under the Uniform Guidelines, a smaller gap can still be adverse impact when it is significant in statistical and practical terms. A larger gap may not be when it rests on a handful of applicants and is not statistically significant. That is why analysts pair the ratio with a significance test.

The Guidelines ask for the check at least once a year, for every group that makes up 2 percent or more of the labor area or workforce. Employers with 100 or fewer employees may keep simpler records. Applicant tracking systems that capture voluntary self-identification data can produce the selection rates for each step.

Example

An employer interviews 100 men and 100 women for warehouse roles and hires 50 men and 30 women. The women's selection rate is 0.30 and the men's is 0.50, so the impact ratio is 0.30 divided by 0.50, or 0.60. That is under the 0.80 line, so the employer reviews the interview step and tests whether the gap is statistically significant.

How it differs from similar terms

Four-Fifths Rule vs Adverse Impact. Adverse impact is the outcome: a substantially different selection rate that disadvantages a group. The four-fifths rule is one quick calculation used to flag it, and the Uniform Guidelines say a gap can be adverse impact even when it passes the rule.

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Frequently asked questions

What is the four-fifths rule in HR?

It is the test HR and compliance teams use to spot adverse impact in a selection step. You compare each group's selection rate with the highest group's rate. A ratio below 0.80 is generally treated as evidence of adverse impact, which calls for a closer look at that step.

How do you calculate the four-fifths rule?

Divide the number selected by the number of applicants for each group to get its selection rate. Take the highest rate as the reference. Divide each other group's rate by the reference rate. Any ratio under 0.80 fails the screen.

What is a 4/5ths rule example?

Suppose 45 of 90 male applicants pass a test and 21 of 60 female applicants pass. The rates are 0.50 and 0.35, so the ratio is 0.35 divided by 0.50, or 0.70. Because that is below 0.80, the test is flagged and the employer checks whether the gap is statistically significant.

Is failing the four-fifths rule proof of discrimination?

No. It is a screening standard, not a legal conclusion. The Uniform Guidelines say a larger gap may not be adverse impact when it rests on small numbers and is not statistically significant. A flag means the employer should examine the step and its job relevance.

How often should employers run the four-fifths test?

The Uniform Guidelines expect adverse impact determinations at least once a year. Many employers also run them whenever they change a test, an interview step or a screening rule, because a new step can shift selection rates quickly.

Which groups does the four-fifths rule compare?

Race, sex and ethnic groups. The yearly check covers each group that makes up at least 2 percent of the labor force in the relevant area or of the workforce. Employers with 100 or fewer employees may keep a simpler set of records.

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