MedCalc Online Statistical Calculators

MedCalc's free online calculators require no registration and are separate from its desktop application. The relative-risk tool takes exposed/control event and non-event counts in a 2×2 table, returning a risk ratio, 95% interval, P and NNT information. Its ratio compares event probabilities a/(a+b) and c/(c+d). If zeros prevent the ratio or standard-error calculation, the documented correction adds 0.5 to all four cells. The guide uses log-RR uncertainty and distinguishes NNT for benefit from harm. Preserve group/outcome definitions when recording a research calculation; reversing them changes its interpretation.