For 2020, the employee contributions to the two plans combined are not permitted to exceed $19,500 of regular elective deferrals or Roth contributions and $6,500 plus catch-up elective deferrals or Roth contributions. If you make elective deferrals to your individual 401(k) totaling $26,000 for 2020 you will not be permitted to make any contributions to your permanent employer plan and you will not receive any matching contributions. You'll want your employee contributions to your permanent employer's plan to be sufficient to obtain the maximum available match, then you can allocate the remainder of your $26,000 of employee contributions between the two plans. Unless you have better investment options in the individual 401(k) or the permanent employer's plan limits employee contributions to less than $26,000 (to avoid failing nondiscrimination testing), simplest would be to just allocate all $26,000 of your employer contributions for 2020 to the permanent employer's plan.
Does your individual 401(k) permit employee after-tax contributions? If not, $160,000 of net profit from self-employment is too little to permit a total of employee and employer contributions to the individual 401(k) of $63,500 since your employer contributions are limited to 20% of net earnings from self-employment. Net earnings from self employment are net profit from self-employment minus the deductible portion of self-employment taxes. Without being able to make an after-tax contribution to the individual 401(k) your maximum employer contribution would be $31,571 if you max out the social security wage base at your permanent employer (resulting in the minimum possible deduction for self-employment taxes), a bit less if you don't. And, as mentioned above, any amount you contribute to the permanent employer's plan further reduces the amount that you are permitted to contribute in total to the individual 401(k).
