For 2019 the combined elective deferral and Roth contribution across all of your employers is $19,000, plus, for those age 50 or over in 2019, a $6,000 catch-up, or your total compensation whichever is less. If you are self-employed, the calculation of the maximum employer contribution is rather complex, TurboTax uses the Deduction Worksheet for Self-Employed from Chapter 5 of IRS Pub 560:
https://www.irs.gov/pub/irs-pdf/p560.pdf
For 2020 the combined elective deferral and Roth contribution limit is raised to $19,500 and the catcu-up is raised to $6,500.
