Adverse impact and the four-fifths rule
How US federal agencies screen selection outcomes for unequal impact, with a calculator that runs in your browser. Sources checked 5 November 2026.
The rule
Under the Uniform Guidelines on Employee Selection Procedures, a selection rate for any race, sex or ethnic group that is less than four-fifths (80%) of the rate for the group with the highest rate will generally be regarded by federal enforcement agencies as evidence of adverse impact. Smaller differences can still count if they are significant both statistically and in practice (29 CFR 1607.4(D), Uniform Guidelines).
How to calculate it
- Divide each group's hires by its applicants to get its selection rate.
- Find the group with the highest selection rate.
- Divide each other group's rate by that highest rate. The result is the impact ratio.
- Compare the impact ratio with 0.80.
Try it
Enter your numbers and select Calculate. Nothing is sent anywhere.
A worked example
With the example figures above: group A selects 48 of 120 applicants (40%); group B selects 20 of 80 (25%). The impact ratio is 25 ÷ 40 = 0.625, below 0.80, so the outcome would generally be treated as evidence of adverse impact and should be investigated.
Its limits
- It is a rule of thumb, not a legal test of discrimination.
- With small numbers, one hire can move the ratio a long way; statistical tests are needed.
- Passing it does not show that a procedure is job-related or fair.
- It applies to outcomes; it does not say which part of a process caused them.
Audits in New York City
New York City's Local Law 144 requires bias audits of automated employment decision tools. A state audit published on 2 December 2025 found that the city's enforcement had received two complaints, and that where the city found one instance of non-compliance among 32 companies, auditors found at least 17 potential instances (New York State Comptroller, audit of 2 December 2025).
Not legal advice
This guide is general information, not legal advice. Take advice for each place you hire.
Questions
Does the four-fifths rule apply to personality assessments?
The Uniform Guidelines cover selection procedures used in employment decisions, which can include assessments. Whether a specific use is covered is a legal question for counsel.
Does the calculator store my numbers?
No. It runs in your browser and sends nothing.
Sources
Keep reading
Take the next step.
What adverse impact is, how the four-fifths rule in the Uniform Guidelines works, a free impact-ratio calculator, and its limits. Not legal advice.