This thread, like almost all others on any financial topic is a bit discouraging.
Why doesn't someone with tens or hundreds of thousands of dollars at risk in their business at least spend a few minutes to ascertain a few basic facts? Or maybe hire a CPA for an hour or two?
All of this stuff is available for free on the IRS.gov site. They also have free explanatory publications that they will send out if you can stand to communicate with our mortal enemy.
Having filed many Schedule C returns over the years, based on the last time I looked, a few basic things are true:
1) If you deposit (quarterly) at least 90% of what you wind up owing for the current year, there will be no late-payment penalty.
2) If you deposit 100% of your previous year's liability, there will be no late-payment penalty. No matter how much you may owe for this year.
For instance: Owed 15K for last year? Had a bang-up year this year and owe 40K but only deposited 15K? No problem. No late-payment penalty. Obviously you still owe the rest of the 40K.
3) No matter how much you owe for this year, if you're under-deposited by less than $1K there will be no late-payment penalty.
4) The penalty for underpayment of taxes is interest at whatever rate is being currently charged by the IRS. May change each quarter.
Current rate is 3% per year. Pretty minimal.
SELF-EMPLOYMENT TAX is 15.3% (anyone self-employed has to pay both the employee and employer rates of 7.65%, the tax for Social Security and Medicare) subject to minor adjustments.
The basic lowest net INCOME TAX bracket is 10%, so a single guy with less-than-stellar income and little or no overhead/expenses can safely assume that he's going to owe around 25% of any AGI over about 12,300 and make appropriate deposits.
Which just means he'll probably owe nothing or get a small refund depending on what is actually reported on his return.
Which illustrates that the "guy" in the original post is doing exactly what he should be doing. Which is more than some "guys" do, only to find out later what they should have been doing when they finally get the tax bill they can't pay a year or two later.
25% works until our "guy" makes more serious money, and still has to comply with all of the tax rules, which include escalating income tax rates.
This is not tax or legal advice of any kind. Do your own due diligence. I suspect that most here will agree that asking for tax or legal advice on a public forum makes one look cheap or silly or both and shouldn't be done. It might even be foolhardy.
I hope all of you guys on this board are doing well, Chinese flu notwithstanding!