"TT tells me that I can defer a maximum of $30,240 to my individual 401k account."
$30,240 is the maximum employee elective deferral after making the maximum $7,241 employer contribution, a total of $37,481.
If you contribute all $37,481 as traditional elective deferral and employer contributions to your individual 401(k), that leaves nothing from which to make a contribution to a Roth IRA. However, only the deductible amount of your self-employed retirement contributions reduce the amount of compensation available to support a Roth IRA contribution, so if you make at least $8,000 of your individual 401(k) contributions to the designated Roth account in the 401(k), that will leave enough to support the maximum $8,000 Roth IRA contribution. Your maximum Roth IRA contribution could be limited by your modified AGI based on you filing status. Probably easier to make the contribution to the designated Roth account in the 401(k) as an employee contribution (correspondingly reducing the amount of your traditional employee elective deferral) rather than making it as a Roth employer contribution. Just enter $8,000 as a Roth employee contribution and mark the Maximize box for an individual 401(k).
