55%
Noncompliance rate for sole proprietors
For W-2 wage earners, the IRS estimates roughly 1% noncompliance. For Schedule C proprietorship income — with no employer withholding and no third-party reporting — that figure reaches 55%.
U.S. Dept. of the Treasury, "The Case for a Robust Attack on the Tax Gap" (2021); IRS National Research Program audit data
$539B
In taxes understated on filed returns, per year
The IRS projects a $696 billion gross tax gap for tax year 2022. Underreporting on timely filed returns accounts for $539 billion of that — more than three-quarters — with business income as the primary source.
IRS Tax Gap Projections for Tax Year 2022 (Pub. 5869), released October 2024
>50%
Of the individual gap flows from small-business income
About half of the individual income tax gap accrues to proprietorships, partnerships, and S-corps — income sources where there is little or no third-party data for the IRS to verify what was filed.
U.S. Dept. of the Treasury, citing IRS Tax Gap Studies