If you got a 6-figure commission on one transaction in the 4th Q 2019, you need to quit wasting your time trying to "figure" anything. You are in "at least" the 22% tax bracket. Add to that the 15.3% SE tax you have to pay, and you're paying over 30% on just that one transaction. Send the IRS 30% of that commission "RIGHT NOW" at www.irs.gov/payments, and be done with it.
Then when you complete your tax return you'll be able to enter each of your quarterly tax payments in the "Estimates and Other Taxes Paid" section under the Deductions & Credits tab. This way, you're practically "guaranteed" to get some of that estimated payment refunded to you. Otherwise, if you underpay by to much, you will be assessed an underpayment penalty. With a 6-figure income, that penalty won't be a small amount either.
