Free A/B test significance calculator.
Check if your A/B test result is statistically significant. Paste control and variant numbers to get p-value, confidence interval, and the sample size you still need. In Blu, the Experimentation Lead agent fixes sample size, a guardrail metric, and a stopping rule before a test ships, so underpowered ones don't.
How to use the A/B test significance calculator
It takes three steps and every output renders on this page so you can copy or export it right away.
Enter visitors and conversions
Add the visitor and conversion counts for your control and your variant. Manual counts from any tool are fine.
Check significance
The A/B test significance calculator returns the p-value, relative lift, both conversion rates, and a 95% confidence interval on the difference.
Open it inside Intempt
Push the parameters into an experiment inside Intempt so the Experimentation Lead agent runs the test with a real hypothesis, guardrails, and a defined exit rule.
Use in Claude
Blu AgentWho it's for
- Marketing and growth teams deciding whether to call an A/B test
- Anyone who wants the significance math without a spreadsheet or a Bayesian black box
What's in the download
SKILL.md- The exact two-proportion z-test math (p-value, CI, sample size, days-to-significance) from the browser tool, plus instructions to check for a connected analytics/CRM MCP first, falling back to pasted numbers.
How to install it
- Open Settings, then Capabilities
- Turn on code execution if it isn't already on
- Upload the .zip you downloaded
- Unzip the download
- Drop the folder into
~/.claude/skills/(or.claude/skills/in a project) - Claude Code finds it automatically
your-new-skill/
What you need
- Claude Desktop or claude.ai (Pro, Max, Team, or Enterprise for claude.ai upload)
- Claude Code: no plan restriction
- An analytics or CRM MCP connector is optional - pasted numbers work without one
Try it with
“Use the ab-test-calculator skill to check if my checkout redesign test is significant”“Pull my latest experiment numbers and tell me if I can call a winner yet”
Prefer an instant answer? Run it now above.
What you get from the A/B test significance calculator
What it does on this page, and what it does inside Intempt.
Four numbers in, no tracking setup needed
- Enter visitors and conversions for the control and the variant
- Works with any rate: signups, clicks, demo requests, or bounces
- Counts from a spreadsheet or a dashboard export are fine
A statistical significance calculator that shows its math
- Runs a two-tailed, two-proportion z-test at 95% confidence
- Reports relative lift, the p-value, and both conversion rates
- Adds the 95% confidence interval on the absolute difference
Ship every experiment with a defined hypothesis
- Hypothesis, primary metric, guardrail, and exit rule are all set upfront
- Locked in before a single pixel moves
- No test ships on gut feel
Watch guardrails while the test runs
- You watch the primary metric and every guardrail side by side
- If a variant lifts one metric while it wrecks another, you'll catch it
- The kill switch trips on its own - nobody has to be watching
Questions about theA/B test significance calculator.
Teams love it
They stopped stitching tools andhired one system.
StockInvest
“Acquisition and retention finally feel like one connected motion instead of two separate problems.”
Jim Stromberg
CEO, StockInvest
FieldsUSA“We finally have one system that sees the whole customer journey.”
Eric Gardner
COO, FieldsUSA
Hoperfy“With Intempt, we built a signal-led pipeline driven by real behaviors.”
Tadas Kertenis
Co-founder, Hoperfy
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