If that is the total income then you forgot to subtract the deductible part (half of the 15.3% SE tax from the net self-employed income). $4K * .15 / 2 = $300 that cannot be used for IRA contributions.
The most you can contribute to all of your traditional and Roth IRAs is the smaller of:
For 2018, $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.
For 2019, $6,000, or $7,000 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 ).
See IRS Pub 590A "What is compensation" for details:
https://www.irs.gov/publications/p590a#en_US_2018_publink1000230355
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.**
