Free · Check count data against a Poisson shape

Poisson Chi-Square Fit Checker

Test whether a large list of non-negative event counts departs from a fitted Poisson distribution.

  • Real chiSquaredGoodnessOfFit calculation
  • Private in your browser
  • Text, CSV, and JSON

Try the calculation

This tool uses simple-statistics 7.10.0. Start with the example or enter your own numbers.

Your numbersCommas, spaces, and new lines all work
The library runs in this tab. Your numbers are not uploaded or saved.
Result
Ready for your numbersChoose “Check the Poisson fit” to see the answer.

Powered by simple-statistics 7.10.0, an open-source JavaScript library available under the ISC license.

Three simple steps

How to use it

  1. Enter at least 20 non-negative whole-number counts.
  2. Choose the cutoff before you check the result.
  3. Press “Check the Poisson fit,” then read the plain-language decision.

Your numbers stay on this device

simple-statistics runs inside this browser tab. Bookify does not upload or save your list. The tool explains the calculation, but a number cannot judge data quality, study design, or what caused a pattern.