Calculator for confidence intervals of odds ratio in an unmatched case control study. For example groups of cases and controls studied to assess a treatment or exposure to a suspected causal factor. This calculator works off-line. (IE4)

Programme written by DJR Hutchon. Enter data into the boxes "A","B","C",and "D" or
into boxes "A", "A+B", "C", and "C+D" Enter titles into blank boxes. Clear all values between entering new sets of values using the clear button.

You can experiment with the effect of different values keeping the same totals within each study group. The calculator will adjust the values to keep the totals unchanged.

Title of study















Study groups


B =

A+B =


D =


Odds ratio OR =
95% confidence interval =
A permanent record of the analysis can be obtained by printing the page.

Odds ratio calculator - select your own confidence interval

This calculator is for educational use. It is believed accurate but no responsibility for accuracy of the results is accepted by the author. David J R Hutchon BSc, MB, ChB, FRCOG Consultant Gynaecologist, Memorial Hospital, Darlington, England.
You are welcome to keep this page and use the calculator off-line. I would appreciate an E-mail if you find it useful enough to do so. E-mail to me at
Reference J Martin Bland and Douglas G Altman Statistics Notes: The odds ratio BMJ 2000;320:1468

This calculator will not calculate correctly with zero in any of the boxes. A different approach is required in these circumstances. One method is to estimate the odds ratio using the null hypothesis. Odds ratio calculator using null hypothesis approach