Use last year's 1040 to set your September 15 tax payment

If you use the prior-year safe-harbor method, make the third-quarter estimated tax payment by September 15. If you expect to be short by at least $1,000 after withholding and credits, that payment is the way to avoid a penalty. For a first-time business owner or freelancer facing self employed taxes 2026, the rule is simple: start with the number already on your return, not a guess about this year.

Quarterly estimated taxes for a small business are easiest when you treat them as a scheduled obligation, not a surprise. The safe-harbor method gives you a defensible starting point because it uses a number the government already has. You are not trying to predict every invoice, every write-off, or every slow month. You are setting a payment that protects you while the year unfolds.

Start with the number already on your return

The prior-year safe-harbor method applies an AGI threshold of $150,000, reduced to $75,000 for married taxpayers filing separately. If that income is over $150,000, or over $75,000 if you are married filing separately, use the higher safe-harbor amount. In practice, the method's threshold is $150,000 of AGI, or $75,000 for married taxpayers filing separately.

This method is useful when your income is new, uneven, or hard to forecast. A first-time owner may not know whether the next quarter will be strong or quiet. A freelancer may have a big project and then a gap. The prior-year number gives you a baseline that is easier to defend than an uncertain projection. It also keeps the decision simple: look at last year, check the income threshold, and move the money.

Turn that number into a scheduled payment

Pull last year's total tax from your 1040. You are done when you have a single dollar amount from the total tax line, not the amount you already paid.

Do not use the amount you paid during the year. That number may include deposits, refunds, or payments from a different tax year. The safe-harbor base is the total tax shown on last year's return. If you have multiple returns, use the one that matches the prior tax year you are using for the safe-harbor test.

Choose the safe-harbor amount from the rule above. The step is finished when you have one annual number you can defend without rebuilding this year's books.

If you are unsure which income threshold applies, check the filing status on last year's return. The threshold is tied to that income figure, not business revenue. A business can have high revenue and a lower adjusted gross income after expenses. That distinction matters because the safe-harbor amount follows the income line, not the top-line sales figure.

Split the annual amount into equal quarterly payments. Finish with identical numbers you can track in a separate account.

Keep the quarterly numbers in one place. A spreadsheet, a notebook, or a simple table works. The important habit is to record the amount, the due date, and the date you moved the money. When the third payment arrives, you should not be checking bank statements to remember what you set aside.

Set aside a payment with each paycheck. The habit is working when money moves out of your business account before you spend it.

Move the money before you pay yourself. If the business account is also your checking account, the payment will compete with rent, software, payroll, and everything else. A separate account makes the tax money visible. It also makes the decision automatic: the payment comes out of the tax account, not out of whatever is left at the end of the month.

Schedule the Q3 estimated tax payment before the deadline. If you use EFTPS, the federal electronic tax payment system, schedule the payment by 8 p.m. Eastern Time at least one calendar day before the payment due date. You are done when the payment is scheduled, not when you plan to make it.

Do not rely on a payment being processed on the due date. If you use the electronic payment system, build in the scheduling lead time. If you pay by check or another method, give yourself enough time for the payment to reach the government before the deadline. The safest habit is to finish the payment process early and keep the confirmation.

Do not mix the payment date with the filing date

Wait until the return is filed, and you may miss the payment. For calendar-year S corporations and partnerships, which pass income to their owners, September 15 is also the extended federal filing deadline for Forms 1120-S and 1065, the federal returns for those businesses. That filing date does not change the estimated payment date.

The filing deadline can create misleading timing. If you are waiting for a business return to be finished, remember that the estimated payment is a separate obligation. The payment is based on the tax you expect to owe, not on the final return. For a new business, the return may not be ready, but the payment date still arrives.

If you are in New York, September 15 is also an estimated payment date for the New York State and New York City pass-through entity tax regimes. The state step is finished when a state payment is scheduled alongside the federal one, not left for later.

This article is general information, not tax or financial advice. Consult a qualified professional about your situation.