What percentage of internet users have an ad blocker?

How to get close to this number

Estimate from what you would expect a third of users to do. Ad blocking requires installing something, which immediately excludes the majority of casual users, but it is free, easy and widely recommended. A behaviour with that profile settles somewhere around a quarter to a third of users, which is where it is.

The variance in the explanation is what matters for anyone relying on advertising: well over forty percent among younger and more technical audiences. A site serving developers or students loses a much larger share of impressions than the average implies, and averages are useless for planning when the variance is this structured.

For this project specifically, the figure is a planning input rather than trivia. It is the single biggest unmeasured variable in any ad-funded revenue estimate — blocked impressions are invisible to the publisher, so projected revenue based on traffic is systematically optimistic by roughly this fraction before any other assumption is tested.