Did B actually win?

The new button got 6.0% and the old one got 5.0%. Is that real, or is it Tuesday? This calculator answers it with the same two-proportion z-test the big testing tools use, in a spreadsheet you can read.

Works in Google Sheets and Excel.

FIVE INPUTS

Visitors and conversions for A, visitors and conversions for B, and your confidence level.

WHAT COMES OUT

• Verdict: B WINS, A WINS, or NOT SIGNIFICANT YET
• P-value (two-tailed), both conversion rates, relative lift, z-score
• The visitors per variant you needed to confirm this lift at 80% power, so you know whether to trust it or keep running

THE PLANNING TABLE

How many visitors per variant you need to detect a 5, 10, 15, 20, 30 or 50 percent lift from your current rate. Decide the sample size before the test, not after.

What you get

• The calculator (.xlsx, opens in Google Sheets or Excel)
• A 1-page quick-start guide

Who it's for

Marketers, product managers, founders and indie hackers running tests without a data scientist to ask.

Good to know

• Formulas are visible, not hidden. Check the maths if you like.
• No macros, add-ons or sign-ups. Works in Google Sheets (free) and Excel 2016 or newer.
• Instant download.

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