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A/B Test Duration Calculator

Work out how long an A/B test must run to reach its required sample size.

About A/B Test Duration Calculator

Duration follows directly from required sample size and traffic. Tests should always run in whole weeks because conversion behaviour differs systematically between weekdays and weekends. Adding variants divides traffic and extends duration proportionally, which is why multivariate tests so often prove impractical.

Formula

A/B Test Duration

Duration = required sample per variant ÷ (daily visitors × allocation ÷ variants)

weekly cycles
Behaviour varies by day, so tests should span whole weeks

Worked example

With the default values below, A/B Test Duration Calculator returns Test Duration of 7.50. Change any input above and every figure here is recalculated in your browser.

Inputs used

Sample size needed per variantminimum 1
15,000
Daily visitorsminimum 1
4,000
Share of traffic in the testaccepts 0–100 %
100 %
Number of variantsaccepts 2–10
2

Results

Test Duration
7.50 days
Test Duration
1.071 weeks
Visitors per Variant per Day
2,000.0
Total Visitors Needed
30,000
Verdict
Practical test duration

Step by step

  1. 1Values used
  2. 2A/B Test Duration
  3. 3Test Duration= 7.50 days
  4. 4Test Duration= 1.071 weeks
  5. 5Visitors per Variant per Day= 2,000.0
  6. 6Total Visitors Needed= 30,000
  7. 7Verdict= Practical test duration

Assumptions and limits

  • The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 3 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

How is A/B Test Duration calculated?

Duration = required sample per variant ÷ (daily visitors × allocation ÷ variants) Duration follows directly from required sample size and traffic. Tests should always run in whole weeks because conversion behaviour differs systematically between weekdays and weekends.

Why does A/B Test Duration matter?

Adding variants divides traffic and extends duration proportionally, which is why multivariate tests so often prove impractical.

What values do I need to enter?

This calculator takes 4 inputs: Sample size needed per variant, Daily visitors, Share of traffic in the test, Number of variants. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.

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