Free tools
Four small, honest calculators for planning, reading and sanity-checking experiments. Instant results, the formula shown under each one, your inputs kept in the link, and no email wall.
Before the test
How many visitors you need to detect a given lift, and how many days that takes at your traffic. The same method as the planner inside the plugin.
After the test
Is the difference real? A two-proportion z-test with a plain verdict, the two conversion rates, the uplift and the confidence, the same test Pro runs on live results.
During the test
Is the traffic split what you set? A chi-squared check that tells you whether an imbalance is normal variation or a broken test you should not read.
Any time
Your conversion rate, revenue per visitor and average order value, plus what a given uplift would be worth per period and per year.
How they fit together: size the test before it starts, check the split while it runs, judge the result when it ends, and put a number on the lift any time.
Prefer this inside WordPress? The free plugin includes a sample-size & duration planner, and Pro computes significance on your live results automatically. New to testing? Start with the guides.
The free plugin plans your tests and checks their traffic split; Pro reads them for you - significance and Bayesian probability.