The September 15 Estimated-Tax Deadline: What Every LLC Owner Files This Week

Updated: August 2026 · Industry Advisors · Education, not legal or tax advice.

The third quarterly estimated-tax deadline lands on September 15, 2026. If you own an LLC and pay taxes through your personal return — which is most LLC owners — this is one of four dates each year the IRS expects to hear from you. Miss it and the underpayment penalty starts accruing the next day. Nail it and there is nothing to do until January.

Here is what this deadline actually is, who owes it, and how to compute the number before the week ends.

What September 15 actually is

The United States runs on a pay-as-you-earn tax system. W-2 employees satisfy that through withholding on every paycheck. Owners of pass-through entities — sole proprietors, single-member LLCs, multi-member LLCs, and S-Corps — pay it directly, four times a year, through estimated-tax payments.

The four due dates for the 2026 tax year:

• April 15, 2026 — Q1 (income earned January through March)
• June 15, 2026 — Q2 (April and May)
• September 15, 2026 — Q3 (June, July, August)
• January 15, 2027 — Q4 (September through December)

Note the asymmetry: the "quarters" are not equal calendar quarters. Q2 is two months, Q3 is three, Q4 is four. It is a quirk of the tax code and it catches new founders every year.

Who owes on September 15

You owe an estimated payment if any of the following are true:

• You are a single-member LLC filing Schedule C or Schedule E on your personal return, and you expect to owe more than $1,000 in federal tax for 2026 after withholding and credits.
• You are a partner in a multi-member LLC that files Form 1065 and issues K-1s.
• You elected S-Corp status and take a reasonable salary plus distributions — payroll covers the wages, estimated tax covers the distribution portion.
• Your LLC elected C-Corp status and expects to owe more than $500 in federal corporate tax for the year (Form 1120-W).

If your only income runs through a W-2 with proper withholding and your side LLC has been quiet, you may owe nothing. Run the safe-harbor test below to be sure.

How much to send — the safe-harbor rule

You are not required to be precise. The IRS gives you two safe harbors that shield you from the underpayment penalty as long as one is met by year-end:

1. 100% of last year's total federal tax liability, paid in four equal installments. (110% if your prior-year adjusted gross income was over $150,000.) This is the safest and simplest method.
2. 90% of the current year's projected tax liability, paid in four installments. Use this if your income is significantly lower than last year and you'd rather not overpay.

If you paid the safe-harbor amount through Q1 and Q2, your Q3 payment is simply one-quarter of the annual safe-harbor number. If you did not — for example, if you missed Q1 — you can catch up on September 15 with a larger payment.

Reasonable ballpark ranges to expect, based on typical single-member LLC profiles (federal only, before state):

• LLC netting ~$50,000 profit — Q3 payment usually $2,500–$4,000
• LLC netting ~$100,000 profit — Q3 payment usually $5,500–$8,500
• LLC netting ~$200,000 profit — Q3 payment usually $12,000–$18,000

These are estimates and vary widely with self-employment tax, S-Corp election, deductions, and credits. Confirm your number with a licensed tax preparer before wiring.

Where to pay

Three official channels, all free:

1. IRS Direct Pay — pay directly from a bank account at irs.gov/payments. No account, no fees, immediate confirmation.
2. EFTPS (Electronic Federal Tax Payment System) — the older enrollment-based system. Setup takes about a week, so if you have not already enrolled, use Direct Pay for September 15 and enroll in EFTPS for January.
3. IRS2Go mobile app or debit/credit card — card payments carry a processor fee (typically 1.75–1.99% of the payment).

Whichever channel you pick, select Estimated Tax (Form 1040-ES) and the tax year 2026. Save the confirmation number in the same folder as the payment record. You will need it in April.

What happens if you miss September 15

The IRS does not send a bill or a reminder. The penalty accrues quietly on Form 2210 when you file your return next April.

The underpayment penalty is calculated as an interest charge on the shortfall. The federal short-term rate plus 3% is the running formula. For most of 2026 that has been in the 7%–8% annualized range. On a $5,000 missed Q3 payment held for seven months (September to April), the penalty runs roughly $200–$250.

Not catastrophic. But if you missed Q1, Q2, and Q3, the penalty compounds and the shortfall on your April 15 return can turn into a five-figure surprise. The safer move is to send something on time, even if it is not perfect.

State side — do not forget

Most states with income tax mirror the federal schedule. Three of the largest:

• California (FTB) — Q3 due September 15. Franchise Tax Board Form 540-ES.
• New York (DTF) — Q3 due September 15. Form IT-2105.
• Illinois (IDOR) — Q3 due September 15. Form IL-1040-ES.

Texas, Florida, Washington, Nevada, South Dakota, Wyoming, and Tennessee have no personal income tax, so LLC pass-through owners in those states file federal only. Washington still has a Business & Occupation tax that runs on a different schedule.

The 30-minute Q3 checklist

1. Pull last year's Form 1040, line 24 (Total Tax). This is your safe-harbor base.
2. Multiply by 100% (or 110% if last year's AGI was over $150,000). Divide by four.
3. Subtract what you already paid through Q1 and Q2.
4. The remainder is your Q3 payment.
5. Log in to IRS Direct Pay. Select 1040-ES · 2026. Send.
6. Repeat with your state's estimated-tax portal.
7. Save both confirmation numbers to your bookkeeping folder.

That is the whole exercise. Thirty minutes, twice a year for the summer and winter payments, three times if you count the April combined return.

Where this fits in the bigger compliance picture

Estimated tax is one of twelve recurring compliance items every LLC owner runs each year. The others include the annual report, franchise-tax filing, sales-tax remittance, payroll deposits (if you have employees or an S-Corp salary), registered-agent renewal, business-license renewal, insurance renewal, K-1 issuance for multi-member LLCs, 1099 filings, and the year-end books close. Miss any of them and the penalties stack.

The Everyday Owner's Blueprint lays all twelve out on a single 12-month calendar with the exact filing links and payment addresses — so nothing quiet accrues in the background.

Industry Advisors provides business formation and compliance education from 30 Wall Street, New York, NY 10005. This article is for educational purposes and is not legal, accounting, or tax advice. Confirm your specific numbers and filing obligations with a licensed professional before you pay.