How does the IRS decide if I earn too much to contribute directly to a Roth IRA?

Eligibility is based on your modified adjusted gross income and filing status. The IRS sets a phase-out range each year: below it you can contribute the full amount, within it your allowed contribution shrinks, and above it you can't contribute directly at all. Married filing jointly has a higher range than single filers, while married filing separately has an unusually low threshold that blocks most people. If you're in the phase-out zone, you can make a reduced contribution using the IRS worksheet. Those above the ceiling typically use the backdoor Roth instead. Because these numbers rise with inflation most years, always check the current thresholds at irs.gov before contributing.