A/B Testing Uptime (Monthly) Calculator FAQ
Answers to common questions about comparing control and variant uptime and estimated monthly downtime.
This FAQ explains the inputs, results, assumptions, and practical interpretation of a monthly A/B testing uptime comparison.
General questions
Basic definitions and uses of the calculator.
What does this calculator compare?
It compares estimated monthly downtime for a control and variant using their uptime percentages.
What is uptime?
Uptime is the percentage of a measurement period during which a service is available.
What is downtime?
Downtime is the portion of the period when the service is unavailable under the uptime measurement definition.
Calculation questions
How the downtime estimates are produced.
How many minutes are in a 30-day month?
There are 43,200 minutes in a 30-day month.
How is control downtime calculated?
Monthly minutes are multiplied by one minus the control uptime divided by 100.
How is the downtime difference calculated?
Variant downtime is subtracted from control downtime.
What does a negative downtime-saved result mean?
It means the variant has more estimated downtime than the control.
Accuracy and interpretation
Important context for reading results.
Does higher uptime prove the variant is better?
No. Availability is one metric and should be interpreted with other test evidence.
Why might observed results differ from the estimate?
Uptime can vary by time period, traffic segment, region, incident type, and monitoring coverage.
Does this tool measure latency or errors?
No. It estimates unavailable time only from the uptime values entered.
Inputs and use cases
Choosing appropriate values for a comparison.
Should both uptime values cover the same period?
Yes. Comparable periods and monitoring definitions make the comparison more meaningful.
Can I compare a short test period?
You can enter the relevant number of days, but short periods may be less representative of longer-term availability.
Should planned maintenance be included?
Use uptime values that consistently include or exclude maintenance for both versions.
How much downtime is 99.9% uptime in 30 days?
It is about 43.20 minutes because 0.1% of 43,200 monthly minutes is unavailable.
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