Yes..apply to 1040ES. You can pay whenever you want. Or just change your job withholding.. or do a little of both. Payments are applied in quarters, but you can pay 100 times a year if you wanted to. Pls use calculation in my original response to reflect projected net income after expenses. So, if 300 doesn't include expenses, you'll want to guesstimate expenses too.. or you may overpay these estimates.
