You can make DISCRETIONARY contributions of up to $19,000 for 2019 as an employee (or $25,000 if you’re 50 or older), even if that is 100% of your self-employed earnings for the year.
In addition, you can contribute up to 25% of your net self-employment income as an employer (business income minus half your self-employment tax) at a maximum considered compensation of $280,000.
Some solo 401(k) providers offer a Roth 401(k) option that allows you to invest some or all of your contributions on an after-tax basis. Not to mention the capability to roll funds in, and borrow from the plan.
ADDITIONAL CONTRIBUTIONS/ROTH CONVERSION
If you’re profit sharing and Employee contributions aren’t enough, make a possible after-tax contribution to max out the 56k limit, and execute a Roth conversion.
DEFINED BENEFIT PLAN FOR HIGH EARNERS
Once you’ve maxed out your Solo 401(k), go for extra credit and look into a Defined Benefit Pension Plan. This supersized retirement plan may allow you to contribute an additional $100,000 pre-tax per year depending on your age and income.