September estimated taxes can sneak up on business owners. Summer schedules change, revenue may rise or fall, and tax planning can easily move to the bottom of the list. But waiting until the last minute can leave you guessing about what to pay and whether your numbers are accurate.
For 2026, the federal third estimated tax payment is due September 15 for income earned during the June 1 through August 31 payment period. This makes September a good time to review your income, expenses, bookkeeping, and expected tax liability.
A quick review now can help you make a more informed payment, protect your cash flow, and avoid an unpleasant surprise later.
September Estimated Taxes: Know What Is Due
The first step is knowing which deadline applies to you.
The IRS generally divides estimated taxes into four payment periods. For 2026, the payment covering June 1 through August 31 is due September 15. Calendar-year corporations also generally make their third estimated tax installment on September 15.
Estimated taxes often apply to business owners whose income does not have enough tax withheld during the year. This can include sole proprietors, partners, and S corporation shareholders.
Federal taxes work on a pay-as-you-go system. That means the IRS generally expects taxes to be paid as income is earned rather than waiting until the annual return is filed.
If you are unsure whether the September deadline applies to your situation, do not guess. Your business structure, income, withholding, and other factors can all affect what you need to pay.
This is a good point in the year to review your situation with a CPA or business tax advisor before sending a payment.
Check Whether You Need to Make an Estimated Payment
Not every business owner handles estimated taxes the same way.
According to the IRS, individuals, including sole proprietors, partners, and S corporation shareholders, generally need estimated tax payments if they expect to owe at least $1,000 when their return is filed after withholding and refundable credits are considered.
Corporations generally make estimated payments if they expect to owe $500 or more in tax.
Those numbers are useful starting points, but they do not tell the whole story. Your prior-year tax, current-year income, withholding, credits, and changes in your business can affect how much you should pay.
This is why September estimated taxes should not automatically be based on whatever you paid last quarter.
If your income has changed, your estimated payment may need to change too. A strong quarter, a large sale, new investment income, or other changes could increase your expected liability. A slower period or larger deductible expenses could move the numbers in the other direction.
Craig Weinstock CPA works with business owners who want to take a more proactive approach to business tax advisory instead of waiting until filing season to find out where they stand.
Review Your Income and Expenses Before Calculating the Payment
Your estimated tax calculation is only as useful as the numbers behind it.
Start by reviewing your year-to-date income. Compare what you have earned so far with what you expected at the beginning of the year. If business has been stronger or slower than planned, your earlier tax projection may no longer be accurate.
Next, look at your expenses.
Check large purchases, payroll costs, contractor payments, business insurance, software, professional fees, equipment, and other expenses that may affect your taxable income. Make sure those expenses have actually been recorded before relying on your financial reports.
This is also a good time to look for unusual changes. Maybe expenses increased during the summer. Perhaps you added employees, purchased equipment, or opened a new revenue stream.
Your tax planning and projections should reflect what is happening in your business now, not what you thought would happen several months ago.
When your income changes throughout the year, reviewing the numbers before each estimated payment can help you stay closer to your actual tax obligation.
Make Sure Your Bookkeeping Is Current
Good tax planning starts with clean records.
If your bookkeeping is several months behind, it becomes much harder to estimate your tax liability accurately. Missing income, duplicate expenses, unreconciled bank accounts, or incorrectly categorized transactions can all change the picture.
Before making your September payment, check that your income and expenses are current. Review your bank and credit card accounts and make sure transactions have been reconciled.
You should also look at accounts receivable if customers owe your business money. Depending on your accounting method, timing can affect how income is reported.
Accurate bookkeeping services do more than prepare you for tax season. Clean records help you see how the business is performing and give your CPA better information to use when preparing tax projections.
If your books have fallen behind over the summer, September is a good time to catch up. Waiting until year-end can make both tax planning and filing more stressful than they need to be.
Protect Your Cash Flow While Preparing for Taxes
Paying estimated taxes is important, but so is keeping enough cash available to run your business.
Before the deadline, review what your business will need over the next several weeks. Look at payroll, rent, inventory, vendor bills, debt payments, insurance, and other regular expenses.
Then compare those needs with the estimated tax payment you expect to make.
This is where planning ahead matters. If taxes consistently create a cash crunch every quarter, the issue may not be the tax payment itself. The business may need a better system for setting money aside as revenue comes in.
Some owners create a separate reserve specifically for taxes. Others use regular tax projections to estimate future payments and build those amounts into cash flow planning.
There is no single approach that fits every business. The goal is to know what is coming before the deadline arrives.
A CPA can help you connect your estimated payments with the larger financial picture so taxes do not become an unexpected drain on working cash.
What New Jersey Business Owners Should Check
New Jersey business owners may have state estimated tax responsibilities in addition to federal payments.
The New Jersey Division of Taxation lists September 15 as the third-quarter estimated income tax payment deadline. State payments are separate from federal estimated tax payments, so making one does not automatically take care of the other.
Your state obligations can depend on how the business is structured and how income flows to you personally.
If your business operates in more than one state, things can become more complicated. Income sourced to multiple states may create additional filing or payment responsibilities.
This is another reason to review your tax situation before sending September estimated taxes. A federal calculation alone may not give you the full picture.
If you are uncertain about federal, New Jersey, or multi-state obligations, schedule an appointment before making assumptions about what is due.
Frequently Asked Questions About September Estimated Taxes
When are September estimated taxes due in 2026?
For most calendar-year individual taxpayers making estimated payments, the third 2026 federal payment is due September 15, 2026. It generally covers income earned from June 1 through August 31. New Jersey also lists September 15 as its third-quarter estimated income tax payment deadline.
What happens if I do not pay enough estimated tax?
The IRS may charge an underpayment penalty when required estimated taxes are not paid in enough amounts or are paid late. The exact result depends on your tax situation, payment history, withholding, and other factors.
What if my business income changed since my last payment?
You should review your estimated tax calculation again. The IRS allows taxpayers to recalculate estimated payments when expected income changes. If your business had a much stronger or weaker quarter, continuing to use an old estimate may not make sense.
Can I wait until I file my tax return to pay everything?
Not always. Federal income tax generally follows a pay-as-you-go system. Business owners and others without enough withholding may need to make estimated payments during the year rather than waiting until the annual filing deadline.
Do Not Let the September Deadline Become a Guess
Estimated tax payments are easier to manage when you know what your business has actually earned, what expenses have been recorded, and what tax liability you may be building throughout the year.
Before making your September payment, review your bookkeeping, year-to-date income, upcoming cash needs, and both federal and state requirements. If your business has changed significantly since the last quarter, your tax projection may need to change with it.
Craig Weinstock CPA helps business owners understand their tax position and plan ahead instead of waiting for surprises at filing time. If you want help reviewing your September estimated taxes or planning for the rest of the year, contact the office today to schedule an appointment.