Just another opinion here (and we all know what opinions are like).
I've been self-employed for 15+ years now, and I've found all this calculating stuff for quarterly taxes to be an absolute waste of my time and effort. All I do each quarter is send the IRS 20% from my *GROSS* earnings for that quarter, and call it good. I have found that when I "calculate" my quarterly taxes, it always falls between 19% and 23% of my *GROSS* income for that quarter. So knowing that, I quit wasting my time "calculating" and just send the IRS 20% of the gross income each quarter. I've been doing that for over 10 years.
In the years I've been doing that, at tax filing time I am "ALWAYS" within $1000 of my total tax liability for the year. Only twice in the 15 years I've been in business have I actually owed the IRS at tax filing time, and both times what I owed was less than $500. All other years resulted in a refund.
At tax filing time if what you owe the IRS is more than $1000 or more than 10% of your total tax liability (whichever is *HIGHER*) then, and only then will an underpayment penalty be assessed. I've never paid such a penalty. In the two years I owed the IRS, since it was less than $500 it was no problem to just write the check, pay it, and be done with it. No need to set up payment plans or any of that other crap.
