How to Work Out What You Owe in Quarterly Taxes

01Start with whether you owe anything at all

You are generally expected to make estimated payments if you expect to owe $1,000 or more when the return is filed, after withholding and credits. That threshold is on the IRS estimated taxes page. If you have a W-2 job alongside the business and enough is being withheld there, you may clear the bar without making a single quarterly payment.

02Two taxes, not one

This is the part that catches people in their first profitable year. Self-employment income is hit by income tax and by self-employment tax, which covers the Social Security and Medicare contributions an employer would otherwise split with you. The IRS explains the mechanism. Someone who budgeted only for income tax is short by a wide margin, and finds out in April.

03The order the calculation actually runs in

Estimate net self-employment income for the year. Add other income. Compute self-employment tax on the business portion, and take the deductible half of it as an adjustment. Apply your deductions and arrive at taxable income. Compute income tax. Add the self-employment tax back. Subtract credits and anything already withheld. What is left is the year's liability, and the quarterly payment is a portion of it. Form 1040-ES carries the worksheet.

04Why I usually recommend the shortcut instead

That whole calculation depends on forecasting a year you have not lived yet. The alternative is to base payments on last year's actual tax, which is a known number rather than a guess — and which, done correctly, protects you from the underpayment penalty regardless of how this year turns out. That is the safe harbour, and it is the single most useful thing in this system for anyone with uneven income.

05Set the money aside where you cannot spend it

The mechanical failure I see most often is not a bad calculation. It is a correct calculation followed by the money being gone in month two. A separate account that receives a fixed percentage of every deposit, moved the day the deposit lands, solves more estimated-tax problems than any spreadsheet.

06Where the books come in

Every figure above starts with net self-employment income, and that number is only as good as your bookkeeping. If the books are three months behind, the estimate is fiction — and the correction arrives with a penalty attached. This is the least glamorous argument for current books and the most expensive one to ignore.

This article is general information, not individualized tax, legal, or financial advice. Every situation is different — reach out and we'll look at yours directly.