Let's say my:
Before Tax Income for the year: $10,000
Amount withheld and subsequently paid in income taxes: $2,000 ($1,500 Federal + $500 State)
Employee contribution to Roth 401K plan at work: $7,000
My question is: How much can I contribute to my Roth IRA that year?
$1,000? (After Tax Income - Contributions to other plans)
$3,000? (Total Income - Contributions to other plans)
$6,000? (Total Income up to $6,000/year limit regardless of my contributions to other plans)
In this case your maximum IRA contribution is $6,000, the lesser of the $6,000 annual limit for someone under age 59½ in 2019 or the amount that will appear in box 1 of your W-2, $10,000.
Had your $7,000 of 401(k) contributions been to the traditional account in the 401(k) instead of to the Roth account, the amount that would appear in box 1 of your W-2 would be $3,000 and your maximum IRA contribution (assuming no compensation from another employer) would be $3,000.