Is the Roth eligibility income limit based od gross income or AGI?

Answer 1

It is based on Modified AGI, which is:

From IRS Pub. 590

Your modified AGI for Roth IRA purposes is your adjusted gross income (AGI) as shown on your return modified as follows.
Subtract the following:

Conversion income. This is any income resulting from the conversion of an IRA (other than a Roth IRA) to a Roth IRA. Conversions are discussed under Can You Move Amounts Into a Roth IRA, later.

Minimum required distributions from IRAs, (for conversions only).

Add the following deductions and exclusions:

Traditional IRA deduction,

Student loan interest deduction,

Tuition and fees deduction,

Foreign earned income exclusion,

Foreign housing exclusion or deduction,

Exclusion of qualified bond interest shown on Form 8815,

Exclusion of employer-provided adoption benefits shown on Form 8839, and

Domestic production activities deduction from Form 1040, line 35, or Form 1040NR, line 33.

Answer 2

AGI

Answer 3

AGI