How long should A/B tests run before making decisions?

A/B tests should run long enough to capture full business cycles and reach statistical significance—typically 2-4 weeks minimum. Running tests for at least one full week captures day-of-week variations. Running for 2-4 weeks captures monthly patterns. However, tests should run until statistical significance is reached, which may take longer for low-traffic sites or small expected improvements. Don't stop tests early just because one variant looks better—this leads to false positives. Use statistical significance calculators to determine when results are reliable. Most consultants recommend running tests for at least 2 weeks, longer for low-traffic sites. Patience is key for reliable results.