Capture–Recapture Calculator
Enter first marked count M, second sample count C and recaptured marked count R. Counts must be integers with 0 < R ≤ min(M, C).
A QUICK WALKTHROUGH
How to use this tool
- Enter the three observed counts.
- Calculate the two population estimates.
- Review the assumptions before interpreting the numbers.
Formulas and source
USGS discusses two-sample population estimation and the Lincoln–Petersen model. https://pubs.usgs.gov/of/2008/1363/pdf/OF08-1363_508.pdf
Assumptions and limits
The population must be closed between samples; marks must be retained and must not affect capture or survival. Marked individuals must mix with the population, and individuals must have equal capture probability. Estimates are not observed counts, confidence intervals or ecological management advice.
Local calculation
Inputs are processed in this browser without upload or storage.
GOOD TO KNOW
Common questions
Why is R = 0 rejected?
Both estimators require a positive recapture count under this tool’s contract; no estimate is presented when R = 0.