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Financial literacy
6 min

September 15 Tax Deadline: What Small Business Owners Need to Know About Q3 Estimated Taxes

Learn what small business owners must do to pay Q3 estimated taxes before the September 15 deadline.

Published at | Updated:

Key takeaways

  • September 15 is the deadline for the third quarter of federal estimated taxes.

  • Most self-employed people and small business owners who expect to owe tax must pay.

  • Paying on time, or meeting a safe harbor amount, helps you avoid an underpayment penalty.

  • Building a quarterly routine keeps every deadline predictable and protects your cash flow.

What is the September 15 estimated tax deadline

Estimated taxes work on a pay-as-you-go basis. You pay tax on income as you earn it, not all at once.

The IRS splits the year into four payment periods. September 15 is the quarterly tax payment deadline for Q3 estimated taxes, which cover income earned from June 1 to August 31.

This date rarely moves, so treat it as fixed. If you owe, the money needs to reach the IRS on or before September 15. For a wider view of the year, our small business tax guide walks through each season.

Who needs to make a Q3 estimated tax payment

Estimated tax payments apply to income that isn’t covered by withholding. That includes many small business owners and self-employed people.

You generally need to make an estimated tax payment if you expect to owe at least $1,000 in tax for the year after subtracting any withholding. This often applies to:

  • Sole proprietors and single-member LLC owners

  • Partners and S-corp shareholders

  • Freelancers and contractors paid on a 1099

Most of these earners also owe self employment tax, which covers Social Security and Medicare. If you receive contractor income, it helps to know the difference between a 1099-NEC and a 1099-MISC before you file.

How to calculate your Q3 estimated tax payment

You don’t need to be an accountant to get close. Follow these three steps to estimate what you owe.

Estimate your expected income for the year

Start with your projected net income for the full year. Add up what you’ve earned so far and forecast the rest.

Include self-employment income, and subtract your business expenses. A rough but honest number beats a guess.

Apply the safe harbor rule

Safe harbor estimated taxes protect you from a penalty even if your estimate falls short. In general, you’re covered if you pay 90% of this year’s tax or 100% of last year’s.

Higher earners usually need to pay a larger share of last year’s tax. The exact figures depend on your income, so check the current rules or ask your accountant.

Divide and adjust for the quarter

Once you know your yearly tax, split it across the four periods. The IRS Form 1040-ES worksheet helps you do the math.

Then adjust for any income shift in Q3. If your summer was busier than spring, pay a bit more now to stay on track.

How to pay your estimated taxes before September 15

Once you know how to pay quarterly taxes, the payment itself takes minutes. Choose the option that fits your cash flow.

Pay online with IRS Direct Pay or EFTPS

IRS Direct Pay lets you send funds straight from your checking or savings account for free. There’s no sign-up needed for a one-time payment.

The Electronic Federal Tax Payment System (EFTPS) is another free option from the U.S. Treasury. It works well if you want to schedule payments ahead and keep a record of each one.

Pay by card to protect cash flow

Sometimes the deadline lands at an awkward time for your bank balance. Paying by card lets you meet the deadline while holding onto cash a little longer.

Many owners now use this approach on purpose. Here’s why some small business owners pay taxes with a credit card to smooth out their cash flow.

What happens if you miss the September 15 deadline

Missing the date usually triggers an estimated tax penalty. The IRS charges interest on the amount you underpaid, based on how late the payment is.

The penalty isn’t a flat fine. It’s based on what you owed and for how long. Paying as soon as you can helps limit the cost.

If you missed it, don’t wait for the next quarter. Send your payment now, then build a steadier plan with our money management tips.

How to stay ready for every quarterly tax deadline

The best fix for deadline stress is a simple routine. A little prep each quarter keeps surprises off the table.

Try these habits to stay ahead of every estimated tax due date:

  • Set aside a share of each payment you receive for taxes

  • Save the four estimated tax due dates in your calendar with reminders

  • Keep clean records of income and expenses as you go

For a step-by-step approach, see how to prepare your small business taxes the easy way. Small steps now save scrambling later.

Simplify quarterly tax payments with Melio

Meeting a tax deadline shouldn’t mean draining your account overnight. Melio lets you schedule your estimated tax payments and pay the IRS by card, even when a card isn’t usually accepted.

That means you can hit the September 15 deadline on time while keeping cash on hand for payroll, vendors, and everyday costs. You stay in control of when the money actually leaves your account.

Set up your payment once, get a clear record, and stop worrying about missing the next quarter. Get your first 30 days free and take the stress out of quarterly taxes.

FAQs on September 15 estimated tax payment

Below are answers to frequently asked questions about the September 15 estimated tax payment.

What day in September are quarterly taxes due?

Quarterly taxes for the third period are due September 15. This payment covers income you earned from June 1 to August 31.

Is the IRS still accepting estimated tax payments by check?

Yes, the IRS still accepts payment by check or money order with a Form 1040-ES voucher. Online options like IRS Direct Pay and EFTPS are faster and give you an instant record.

What happens if I miss a quarterly estimated tax payment?

You’ll likely owe an estimated tax penalty, which is based on how much you underpaid and for how long. Paying as soon as possible helps reduce the amount.

What is September 15th for taxes?

It’s the deadline for the Q3 estimated tax payment for many small business owners and self-employed people. It also lines up with certain business return deadlines, so check what applies to you.

This blog post is intended for informational purposes only and is not intended as financial advice. Melio does not provide legal, tax, or accounting advice, and you should consult a professional advisor before making any financial decisions.

This content is for informational purposes only and should not be considered financial, legal, tax, or accounting advice. Melio does not provide professional advisory services. Always consult a qualified professional before making financial or business decisions.

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