TurboTax's page indicating the amount that you are permitted to contribute has never provided a comprehendible breakdown of your permitted elective deferral and employer contribution. It's even worse this year because TurboTax's Keogh, SEP and SIMPLE Contribution Worksheet has not been fully updated with the 2020 elective deferral limits (regular should be $19,500 and catch-up should be $6,500).
Line 9 of the worksheet is simply the section 402(g) limit, but as I said, it hasn't been updated to $19,500 for 2020. However, this lack of update is not affecting the calculation because your net earnings are limiting you to a total contribution of less than $19,000.
If TurboTax is saying that you maximum deductible contribution is $17,937 (worksheet line 21), that amount consists entirely of regular elective deferrals, limited by your net earnings. Net earnings are net profit minus the deductible portion of self-employment taxes (worksheet line 3). Presumably this is the result of having a net profit of $19,301 (assuming that you don't have W-2 income that when combined with income from self-employment would result in exceeding the Social Security wage base above which you no longer pay the Social Security tax portion of self-employment taxes).
In this case all available net earnings are going to elective deferrals and none remains from which to make an employer contribution.
