I forgot to factor in the same limitation that TurboTaxMarylinG mentioned, that your total contributions are also limited to net profit (minus $0 of deductible SE taxes), so the total contributions cannot exceed $26,624. So if you made $4,062 of employer contributions your elective deferrals would be limited to $18,500 of regular elective deferrals and $4,062 of catch-up. After reviewing this again, I think that's what you were saying and is what TurboTax should be calculating.
Yes, whatever portion of the contribution is not deductible, is retained in the account and 10% penalty paid with Form 5330 can be applied toward your 2019 contribution. But with your contributions totaling $5,376 more than permitted, you might have to have a bit higher income in 2019 to be able to apply all of that as an employer contribution for 2019.
