# What is the False Positive Rate?

The False Positive Rate (Fall-out) is a performance metric that measures the probability that your model will predict *positive* when the true value is *negative*.

- It is closely related to the False Negative Rate, which is completely analogous.
- The False Positive Rate and the True Negative Rate sum up to 1.
- The False Positive Rate is the answer to the following question:
**“If the true value is negative, what share did my model predict incorrectly?”** - The False Positive Rate is calculated as follows:

\frac{FP}{FP+TN} = \frac{FP}{N} = 1 - TNR