The IRS estimates there are roughly 10–15 million non-filers in any given year. These are predominantly people at the very bottom of the income distribution — informal/gig workers paid in cash, undocumented workers, people living below the filing threshold (~$13,850 for a single filer in 2023), or people who simply don't engage with the tax system at all. By definition, none of them appear in the IRS percentile data we were discussing, which means every median and threshold figure we've been talking about is drawn from an already self-selected, somewhat more affluent population.

How Much It Would Move the Needle
If you folded in even 10 million people earning, say, $15,000–$20,000 or less, you'd be injecting a large block of very low earners into the bottom of the distribution. The 50th percentile cutoff would shift downward — potentially meaningfully — because you'd need a lower income to still be above half the expanded population.