🔬 Post-Test Probability Calculator
Calculate the post-test probability of a condition given a pre-test probability and a test’s sensitivity and specificity, using Bayes’ theorem.
What is post-test probability?
Post-test probability is the updated likelihood that a condition is present after a test result is known, combining the pre-test probability with how informative the test is (its sensitivity and specificity).
The method
The calculator converts pre-test probability to odds, multiplies by the appropriate likelihood ratio (LR+ = sensitivity / (1 − specificity) for a positive result, or LR− = (1 − sensitivity) / specificity for a negative result), and converts the resulting post-test odds back to a probability using Bayes’ theorem.
This tool is for general educational and statistical planning purposes only and is not a substitute for professional or clinical judgment.