Some of the ten million or so are probably cheats, but Houston CPA Bob Fumagalli says the majority are not.
"I don't think the people are cheating the IRS; I mean, the IRS really doesn't care if you pay in or not, they're just gonna charge a penalty, which is basically interest, if you don't pay it in during the year."
Fumagalli is biased, but he recommends a tax preparer.
"If you want to pay in so you don't have a real ugly situation on April 15th then you do indeed need to work with a professional to arrive at that proper amount."
The IRS believes millions of Americans are simply confused.
But Fumagalli says imposing a simple, flat tax might not help.
"A flat tax for someone making a W2 income is going to be different than a flat tax for someone who's self-employed and that's who we're talking about here with having to make these estimated payments are the self-employed individuals."
Fumagalli says those who have to make quarterly earnings estimates should sit down with a professional to make sure they get it right.