What Is Margin of Error?
How many percentage points a survey's results could differ from the true value in the full population, at a given confidence level.
When a poll reports “62% approve, ±3 points,” the margin of error is that ±3. It means the true figure across the whole population is likely somewhere between 59% and 65%, not exactly 62% — surveys measure a sample, not everyone, so there’s always some uncertainty band around the result.
Margin of error shrinks as sample size grows, but not in a straight line — cutting the margin of error in half requires roughly quadrupling the sample size, which is why very tight margins (±1%) get expensive fast while going from ±5% to ±3% is a more modest jump.
Margin of error is always reported alongside a confidence level (commonly 95%) — the two travel together. “±3 points at 95% confidence” means: if you ran this survey 100 times, about 95 of those times the true value would fall within 3 points of your result.
Example
NPS of 42 with a ±4 margin of error means the true score is most likely between 38 and 46.
How to Calculate Margin of Error for SurveyRock
Use SurveyRock's free sample size calculator to see how margin of error changes as you adjust sample size and confidence level, before you decide how many responses to collect.
Use the sample size calculator