Actually, that's your call. If you "know" (as well as you can "know") what your tax liability will be. Here's how this works.
If, at tax filing time you owe the IRS more than $1000 or more than 10% of your total tax liability, then an underpayment penalty will be assessed for not having paid enough each quarter. That will be based not just on the business income, but on the entire total household income reported on the tax return.
Remember, with self-employment income in addition to your "regular" tax on that specific income, you will also pay the additional 15.3% self-employment tax on top of that.
