Loading…
Loading…
ConfidLab
How much a poll result could be off, purely from sampling.
A poll of 1,000 people can't perfectly represent millions of voters — the margin of error quantifies how much the reported percentage could plausibly differ from the true population value, just from random sampling variation.
Margin of error is largest when the true proportion is near 50% and shrinks as it moves toward 0% or 100% — this is why pollsters often report worst-case margins assuming a 50/50 split.
Margin of error
± 4.9%
Reported result: 50% ± 4.9%
What you entered
Sample proportion variance: p(1−p)
0.5 × (1 − 0.5)= 0.25Standard error
√(0.25 ÷ 400)= 0.025Margin of error
1.96 × 0.025= 0.049Result
Margin of error: ± 4.9%
With a sample of 400 at 50%, the margin of error is ± 4.9 percentage points at 95% confidence.