Free Tool

MDE Calculator

Given your traffic and test duration, what's the smallest improvement your test can reliably detect? Know this before you run — not after.

Minimum Detectable Effect Relative uplift
Total visitors split equally between variants. E.g. 10,000 daily × 14 days ÷ 2 variants = 70,000 per variant.

Or calculate from traffic + duration:

Results will appear here after you click Calculate.

What is MDE and why does it matter?

MDE (Minimum Detectable Effect) tells you the smallest improvement your A/B test can reliably detect given your sample size, baseline CVR, and statistical requirements. It's the "sensitivity" of your test.

A high MDE means your test is "blunt" — it can only detect large changes, and smaller real improvements will appear inconclusive. For low-traffic sites, accepting a higher MDE (20–30%) is often necessary. For high-traffic pages, you can detect smaller changes (5–10%) reliably.

If your MDE is higher than the improvement you expect from your hypothesis, your test is underpowered before it starts. Either increase test duration, focus on a higher-traffic page, or recalibrate your hypothesis.

Not enough traffic to test everything?

We prioritize the highest-ROI experiments for your actual traffic volume — so you stop running underpowered tests that waste months.