About this block

Test Duration Calculator turns three sliders into an honest calendar. Daily visitors, baseline conversion, and the lift you want to detect feed a sample size formula, and the result panel prints the days a test needs, paints them onto a six week grid one square per day, and rounds up to full weeks so weekday swings cancel out. A plain verdict tells the visitor whether the wait is normal or the lift is simply too small.

A client component on the ui Slider with plain useState, the math runs at 95% confidence and 80% power with the formula spelled out in the footnote. Results round up to whole days and whole weeks because a duration quoted to the hour reads as false precision on a page like this.

When to use

Reach for this block on an experimentation or CRO product page where the value is running tests properly rather than fast. Calling a winner early is the most expensive habit in the discipline, and a calendar the visitor built from their own traffic makes the real wait concrete before you ask them to trust your tooling with it.

A natural flow around it on a Marketing Pro page:

Before

• Feature sections walking through the testing workflow this sizes

After

• Case studies showing tests that ran full and shipped a real win
• CTAs while the honest duration is still on screen

What you can display

One strong use is A/B test duration in days. Other experiment framings:

• Sample size. The raw visitors per variant a test needs before days ever enter the picture.
• Multi variant splits. The run stretched across three or four arms instead of a straight A/B.
• Minimum detectable effect. Fix the run length and read back the smallest lift you could catch.

Tip: keep the confidence and power in the footnote, a duration with no assumptions is a guess wearing a number.