You are mixing apples an oranges. There are two Roth limitations. One is earned income and the other is total income.
1) For 2018 you cannot contribute more than $5,500, or $6,500 if you’re age 50 or older by the end of the year; or
your taxable compensation for the year.
(Taxable compensation is generally wages that you worked for - W-2 or net self-employed income minus the deducible part of the SE tax, but can include commissions, alimony and separate maintenance, and nontaxable combat pay ).
2) To be able to contribute to Roth IRA at all, reguardless of whether you have sufficient earned income at much as the contribution, your total MAGI must also be less than the limits for your filing status. All income is part of your AGI including any retirement income that is taxable.
See this IRS article for Roth contribution limits:
https://www.irs.gov/retirement-plans/roth-iras
**Disclaimer: This post is for discussion purposes only and is NOT tax advice. The author takes no responsibility for the accuracy of any information in this post.**
