This is a follow up to the "Independent Contractor - Calculated Taxes" thread posted yesterday.

For a more vivid example of my situation:
1st Monthly Payment (February) - $300
2nd Monthly Payment (March) - $860
No Payment received in January

Do I then perform:
February - $300 x 15.3% (SECA) + $300 x Federal Tax Rate% + $300 x State Tax Rate% = Total to pay Quarterly?
And do the same for March payment as above?
Then take those two new amounts and pay my April 15th quarterly liability?

I will not have estimated income tax withheld from my employer. I received a tax refund this year from my 2016 taxes, which I think means no prior year tax liability. If I am not mistaken, my employer will send a 1099MISC at year end. My question is more so asking what do I withhold during the year to at least not underpay taxes.

Thank you - If possible, please use my example above or similar example; I need the visual. I appreciate all the help.