Fisher Exact Test Calculator
Use Fisher’s exact test for a 2×2 contingency table when counts are small or when a large-sample approximation may be unreliable. Enter integer counts; the calculation conditions on the table margins.
How to use this calculator
- Enter the group 1 outcome present using the units shown beside the field.
- Enter the group 1 outcome absent using the units shown beside the field.
- Enter the group 2 outcome present using the units shown beside the field.
- Review the calculated values and check that the assumptions match your scenario.
- Change one input at a time when comparing scenarios so you can see which assumption drives the result.
Formula and assumptions
For fixed row and column margins, sum hypergeometric probabilities of all feasible tables whose probability is no greater than the observed table (two-sided probability-ordering definition).
- Different software can implement two-sided exact p-values with different conventions. Interpret the value with the study design and report the chosen method alongside the result.
- The result is computed from the values you provide; it does not fetch external rates, live account data or local rules.
Worked examples
Worked example
The example table compares 12/17 versus 7/17 outcomes. The reported two-sided p-value is based on exact hypergeometric probabilities for all feasible tables with those margins.
Example inputs: Group 1 outcome present = 12, Group 1 outcome absent = 5, Group 2 outcome present = 7, Group 2 outcome absent = 10.
Compare the displayed output with your own measurements before using it in a decision.
Understanding the result
Different software can implement two-sided exact p-values with different conventions. Interpret the value with the study design and report the chosen method alongside the result.
Results are estimates based on the stated model. If the situation depends on measured conditions or contractual specifications, use those source values rather than typical assumptions.
Important notes
Different software can implement two-sided exact p-values with different conventions. Interpret the value with the study design and report the chosen method alongside the result.
Frequently asked questions
What formula does this calculator use?
It uses the method described above: For fixed row and column margins, sum hypergeometric probabilities of all feasible tables whose probability is no greater than the observed table (two-sided probability-ordering definition).
What should I verify before relying on the result?
Different software can implement two-sided exact p-values with different conventions. Interpret the value with the study design and report the chosen method alongside the result.
Can I compare different scenarios?
Yes. Change the inputs while keeping units and definitions consistent, and record the assumptions used for each scenario.
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This page provides a calculation tool plus explanatory information so you can understand what the result means and when the underlying method may not fit your situation.