Test Duration Calculator estimates the time required for an to reach . Running tests too short produces unreliable results. Running too long wastes time and resources. Calculators help plan tests with appropriate duration.
What is a Test Duration Calculator?
Duration calculators use statistical formulas to determine how many visitors (or conversions) a test needs. Combined with traffic estimates, this produces a time estimate.
Calculator inputs:
- Current (baseline)
- (smallest change worth detecting)
- Statistical (typically 95%)
- (typically 80%)
- Daily traffic or conversions
- Number of variants
How Duration is Calculated
Sample size depends on:
Sample Size per Variant = f(baseline rate, MDE, significance, power)
Then:
Test Duration = (Sample Size × Number of Variants) / Daily Traffic
Why Duration Matters
Too short: Results may not be statistically significant. Apparent winners could be random variation.
Too long: Delays other tests. Business conditions may change during the test.
Just right: Sufficient data for reliable conclusions without wasting time.
Factors Affecting Duration
Baseline conversion rate: Higher rates need fewer samples to detect changes.
Minimum detectable effect: Smaller effects require more data to detect reliably.
Traffic volume: More traffic means shorter tests.
Number of variants: More variants split traffic, extending duration.
Using Calculator Results
If calculated duration exceeds acceptable limits:
- Increase minimum detectable effect (accept detecting only larger changes)
- Reduce number of variants
- Focus on higher-traffic pages
- Combine with other tests carefully
