September has a way of sneaking up on business owners.
Summer is winding down, Q4 planning is beginning, and suddenly there’s another important date on the calendar: September 15.
For many business owners, September 15, 2026, is the deadline for the third installment of estimated federal income taxes. That includes individuals who are required to make estimated payments, while calendar-year corporations also have a third estimated-tax installment due that day.
But here’s the bigger question:
Are you paying the right amount?
If you calculated your estimated taxes at the beginning of the year and haven’t revisited them since, your original numbers may no longer reflect what’s actually happening in your business.
For law firms and franchise restaurant owners especially, revenue, payroll, operating costs, and profitability can change considerably over the course of a year.
Before making that September payment, it’s worth taking a closer look.
Why the September 15 Deadline Matters
The federal income tax system is generally pay-as-you-go. Instead of waiting until you file your return to pay your entire tax bill, taxes are paid throughout the year through withholding, estimated tax payments, or a combination of the two.
For individuals, the IRS divides estimated taxes into four payment periods, with the third 2026 payment due September 15. If you don’t pay enough by the applicable deadlines, you could face an underpayment penalty—even in some situations where you’re ultimately due a refund when you file.
That doesn’t mean you should simply pay more “just to be safe.”
Overpaying can unnecessarily pull cash out of your business.
The goal is to make an informed payment based on your actual financial situation and applicable tax rules.
Start With Your Year-to-Date Profit
Your bank balance doesn’t tell you how much tax you owe.
Neither does your gross revenue.
A better starting point is reviewing your year-to-date financial statements, particularly your Profit & Loss Statement.
Ask:
- How does 2026 revenue compare with projections?
- Have operating expenses increased or decreased?
- Is net profit higher than expected?
- Have there been any unusual one-time expenses or revenue events?
- Are the books completely up to date?
This gives your tax professional much better information for estimating your potential year-end liability.
For Law Firms
Revenue can be particularly uneven.
A large contingency fee, unexpected settlement, increased collections, or a rapidly growing practice area could push annual income above earlier projections.
On the other hand, delayed client payments, additional hiring, or higher operating expenses may have reduced profitability.
That’s why relying solely on last year’s numbers can give you an incomplete picture.
For Franchise Restaurants
Higher sales don’t necessarily equal higher profits.
If sales increased 10%, but food costs, wages, insurance, royalties, and other operating expenses also increased, taxable profit may tell a very different story.
Look beyond the top-line sales number and review what the business is actually earning after expenses.
Review What You’ve Already Paid
Before determining what to pay in September, confirm what you’ve already paid toward your 2026 federal tax obligation.
That may include:
- Previous estimated tax payments
- Federal income tax withholding
- Prior-year overpayments applied to 2026
- Other applicable tax payments or credits
Don’t assume every payment was made exactly as planned. Verify it.
This is especially important when multiple people are involved in managing the company’s finances.
Understand the Estimated-Tax Safe Harbor Rules
For many individual taxpayers, understanding the general “safe harbor” rules can help reduce the risk of an estimated-tax underpayment penalty.
Generally, most individual taxpayers can avoid the penalty if they owe less than $1,000 after withholding and refundable credits, or if their withholding and estimated payments satisfy applicable thresholds.
One commonly used framework looks at the smaller of 90% of the current year’s tax or 100% of the previous year’s tax. For certain higher-income taxpayers, the prior-year threshold generally increases to 110%.
However, the rules vary based on circumstances and business structure, so don’t assume a general percentage automatically applies to you.
This is an area where working with your tax professional is particularly important.
What If Your Income Isn’t Consistent Throughout the Year?
Not every business earns income evenly.
That’s particularly relevant to the audiences we’re talking about.
A law firm could receive a major fee in August after a relatively quiet first half.
A franchise restaurant in a seasonal market might generate a much larger portion of annual profit during particular months.
The IRS recognizes that income can fluctuate. In some circumstances, taxpayers with uneven income may be able to use the annualized income installment method, which can result in unequal estimated payments based more closely on when income was earned.
This can be valuable, but the calculations are more complicated, so it’s worth discussing with a qualified tax professional.
Don’t Forget About Cash Flow
Tax planning and cash-flow planning should work together.
You don’t want September 15 to arrive and suddenly discover that a significant tax payment is competing with:
- Payroll
- Rent
- Vendor invoices
- Equipment purchases
- Insurance
- Franchise fees
- Other operating expenses
Look several months ahead.
Law Firms Should Consider
Upcoming payroll, partner distributions, technology investments, expected collections, and large case-related expenses.
Franchise Owners Should Consider
Inventory, seasonal staffing, equipment repairs, holiday preparation, vendor costs, and other Q4 expenses.
Your tax obligation doesn’t disappear because cash is tight, but forecasting gives you more time to prepare.
Use September to Start Your Year-End Tax Planning
Your September estimated-tax review shouldn’t end when the payment is submitted.
It’s also an excellent opportunity to forecast the remainder of 2026.
Ask:
What will the business look like by December 31?
Review planned equipment purchases, staffing changes, retirement contributions, deductible business expenses, and other transactions that could affect your tax position.
If you’ve had an unusually strong year, now is the time to find out—not in March or April when the year’s already over.
Likewise, if profitability has declined, updating your projections may help you avoid unnecessarily tying up cash in excessive estimated payments.
Clean Bookkeeping Makes Everything Easier
There’s one requirement behind nearly every strategy we’ve discussed:
Your books need to be accurate.
If you’re making a September tax decision using financial statements that haven’t been reconciled since May, you’re working with incomplete information.
Before reviewing estimated taxes:
✔ Reconcile bank and credit card accounts.
✔ Confirm revenue has been recorded accurately.
✔ Review payroll entries.
✔ Categorize outstanding transactions.
✔ Verify major purchases and expenses.
✔ Review accounts receivable and payable.
Clean bookkeeping gives you a clearer picture of what your business has actually earned—and that makes tax planning far more useful.
The Bottom Line
The September 15 estimated-tax deadline shouldn’t simply be another date when you send a payment because your calendar tells you to.
Use it as a financial checkpoint.
For law firms and franchise restaurant owners, September is an ideal time to review:
- Year-to-date profitability
- Previous tax payments
- Revenue and expense changes
- Cash-flow needs
- Estimated year-end income
- Opportunities for Q4 tax planning
A lot can change between January and September.
Your tax strategy should be able to change with your business.
Are You Paying the Right Amount?
If you’re unsure whether your September estimated-tax payment still reflects your current financial situation, now is the time to find out.
Contact us today to schedule a bookkeeping and tax-planning review. We can help you review your year-to-date financials, identify potential issues, and work with you to prepare for the September 15 deadline and the final months of 2026.
The goal isn’t simply to get another tax payment out the door.
It’s to understand your numbers, protect your cash flow, and enter Q4 with a clearer financial plan.