Statistics & Probability

Instant, private, and free

False Positive Calculator.

Calculate this statistic instantly with validated formulas.

On-device calculationNo signup
01

Set your values

Results update as you type.

Result: P(condition | positive): 16.6667%

Result

P(condition | positive): 16.6667%

Use Cases

Evaluate diagnostic test accuracy

Use the false positive rate to assess how often a diagnostic test incorrectly identifies healthy individuals as having the condition.

Example: If a test has 5 false positives and 95 true negatives, the FPR is 5%.

Compare classification models

In machine learning, compare the false positive rates of different models to choose the one with fewer false alarms.

Example: Model A has FPR 0.03, Model B has FPR 0.08, so Model A is better.

Frequently Asked Questions

What is a false positive?
A false positive occurs when a test incorrectly indicates the presence of a condition (e.g., a disease) when it is actually absent. In statistics, it's a Type I error.
How is the false positive rate calculated?
The false positive rate (FPR) is calculated as the number of false positives divided by the sum of false positives and true negatives (FPR = FP / (FP + TN)). This calculator uses your input values to compute this rate.
What values do I need to enter?
You need to enter the counts for false positives (FP) and true negatives (TN), separated by commas or spaces. The calculator will then compute the false positive rate.

Tips & Common Mistakes

Tips

  • Ensure your values are counts (non-negative integers) for accurate results.
  • Separate values with commas or spaces; avoid mixing them.
  • Double-check that you are entering false positives and true negatives, not other confusion matrix values.
  • Use the false positive rate alongside other metrics like sensitivity and specificity for a complete picture.

Common Mistakes to Avoid

  • Entering percentages instead of raw counts (e.g., 5% instead of 5).
  • Confusing false positives with true positives or false negatives.
  • Using negative numbers or decimals when counts are required.

Last updated: August 13, 2026