Why This Exists
Because every product team has been there: promising a test will "only take a couple weeks," then watching weeks turn into months while stakeholders ask daily if it's done yet.
This calculator uses standard statistical formulas to tell you the truth up front. No sugar coating. No optimistic timelines. Just math.
Who Made This?
Built by Noah Manion, after too many meetings where someone said "can't we just test it real quick?"
The Math
We use the standard two-proportion z-test formula for sample size calculation. It's the same math everyone uses—we just don't lie about the implications.
For statistical significance testing, we apply a two-tailed z-test with proper methodology for multiple variants.
Is This Free?
Yes. No signup, no paywall, no "basic plan." Just a calculator.
Need Help With Experimentation?
If you're struggling to run tests at scale or need help building an experimentation program, I work with teams through Softpath. I focus on helping teams understand how to run proper A/B tests, interpret results correctly, and build sustainable experimentation culture.
Open Source
The code is on GitHub. MIT licensed. Do whatever you want with it.
Contact
Questions, bugs, or feedback? Find me at softpath.com.