Odds Ratio & Relative Risk Calculator
Enter values into the 2×2 contingency table to calculate OR, RR, ARR, NNT and 95% confidence intervals.
2×2 Contingency Table
| Cases / Disease+ | Controls / Disease− | |
|---|---|---|
| Exposed / Risk factor+ | a | b |
| Unexposed / Risk factor− | c | d |
a = exposed cases | b = exposed controls | c = unexposed cases | d = unexposed controls
Use OR for case-control studies. Use RR for cohort studies and RCTs.
Results
Enter values in the table to see results
Formula reference
Odds Ratio (OR)
(a × d) / (b × c)
Case-control studies
Relative Risk (RR)
[a/(a+b)] / [c/(c+d)]
Cohort studies, RCTs
NNT
1 / ARR
Number needed to treat
For educational and research purposes. Source: Schlesselman JJ. Case-Control Studies. Oxford University Press, 1982. Reviewed Sep 2026.