Odds Ratio Calculator
Odds ratio with confidence interval, z-test and Fisher's exact p from a 2×2 table.
Enter your values to see the result.
Uses Woolf's logit method for the confidence interval and adds 0.5 to every cell when one of them is zero (Haldane–Anscombe correction). Results use standard large-sample formulas and are meant to support, not replace, a statistician's review. Check the assumptions behind each method before you report the numbers.
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- Relative Risk Calculator — Use relative risk for cohort studies and trials.
- 2×2 Contingency Table Calculator — Add chi-square and Fisher’s exact tests.
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Clear instructions
Find steps, examples and limitations below.
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How to use the Odds Ratio Calculator
Odds ratio with confidence interval, z-test and Fisher's exact p from a 2×2 table.
- 1 Enter exposed and unexposed counts for cases and controls.
- 2 Pick the confidence level.
- 3 Read the odds ratio, its confidence interval and the p-values.
Example and practical tips
With 40 exposed and 20 unexposed cases against 60 exposed and 80 unexposed controls, the odds ratio is 2.67 (95% CI 1.42 to 5.02).
Frequently asked questions
When should I use an odds ratio instead of relative risk?
Use the odds ratio for case-control studies, where you choose people by outcome and cannot measure risk directly. It also comes out of logistic regression.
What if a cell is zero?
The odds ratio would be zero or infinite, so 0.5 is added to every cell (the Haldane–Anscombe correction) and a note is shown.
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