Odds Ratio Calculator

About this calculator

This calculator finds the odds ratio, OR = (a·d)/(b·c), from a 2×2 contingency table cross-tabulating exposure (or treatment) against outcome, where a and d are the concordant cell counts and b and c are the discordant ones. An OR of 1 means no association between exposure and outcome, an OR greater than 1 means the exposed group has higher odds of the outcome, and an OR less than 1 means lower odds — it's the standard measure of association in case-control studies, where relative risk can't be calculated directly.

Epidemiologists and medical researchers use it constantly to quantify how strongly a risk factor — smoking, a genetic variant, an environmental exposure — is associated with a disease or outcome, and it's the statistic most commonly pooled across studies in meta-analyses. Public health students, biostatisticians, and authors of systematic reviews all rely on this calculation when reading or reporting case-control study results.