What is Confidence Interval?
A confidence interval is a range of values that is likely to contain the true figure, given the uncertainty in your sample.
Confidence Interval explained
If you estimate a conversion rate from a sample of visitors, the true rate for all visitors is probably a little different. A 95 percent interval is a range calculated by a method that captures the true value 95 percent of the time over many repeated samples.
Wide intervals warn that the sample is small or noisy. Reporting an estimate without any range suggests more certainty than the data can support.
Example
A conversion rate of 4.1 percent with a 95 percent interval of 3.6 to 4.6 percent tells you the true rate is probably within that band.