The Internal Revenue Service is worried: Too many Americans are underreporting their income, either deliberately or by making mistakes on their tax returns.

The net result, the IRS reports, is that there is a “tax gap” between what’s owed and what’s actually paid that amounts to as much as 16 percent of federal taxes going uncollected.

The last survey of the problem is a full decade old, and estimates from 2001 say $345 billion was going uncollected then. Today, the amount could be between $410 billion and $500 billion, and the IRS is planning another study within a year or so.