Self-Employed? Prepare Now for Your September Tax Deadline

If you’re self-employed, freelancing, or running your own small business, your tax responsibilities look very different from those of traditional employees. One key difference? You’re expected to pay estimated taxes four times a year—and the next big deadline is in September. September 16, 2025, marks the third quarterly estimated tax payment for the 2025 tax year. Missing this deadline can lead to interest charges and penalties, even if you end up getting a refund when you file next year. The good news? Preparing now gives you time to organise, plan, and avoid unnecessary stress. Here’s what you need to know to stay ahead.

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What Are Quarterly Estimated Taxes?

When you’re self-employed, the government doesn’t withhold income tax from your earnings like it does for employees. Instead, the IRS expects you to pay taxes on your income as you earn it—and that’s where quarterly estimated payments come in. Each year, self-employed individuals must make estimated payments in April, June, September, and January for the previous quarter’s earnings. These payments cover both income tax and self-employment tax, which includes your contributions to Social Security and Medicare.

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Who Needs to Pay Estimated Taxes?

You’re generally required to make estimated payments if you expect to owe at least £1,000 ($1,000) in federal taxes when you file your return. This applies to:

• Sole proprietors
• Freelancers and contractors
• Partners in a business
• Gig economy workers
• Anyone earning untaxed income regularly

If you’ve received income in July or August with no tax withheld—whether it’s from client work, digital sales, or consulting—you’ll need to include it in your September 16 payment.

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How to Calculate Your September Payment

To avoid underpayment penalties, aim to pay at least 90% of your expected total tax bill for the year, or 100% of what you owed last year (whichever is smaller). To calculate your payment:

1. Estimate your year-to-date income.
2. Subtract your business expenses to find your taxable income.
3. Use the IRS Schedule SE to determine self-employment tax.
4. Apply the appropriate income tax rates.
5. Divide the total by four to get your quarterly amount.

This can feel overwhelming, but using a Tax Refund Calculator or working with an accountant can make it easier and more accurate.

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Track Business Expenses Now—Not Later

Accurate expense tracking is one of the best ways to reduce your taxable income and lower your quarterly payment. Start reviewing your receipts and records now. Eligible deductions may include:

• Home office expenses
• Internet and phone costs
• Software and tools
• Travel and mileage
• Marketing and advertising
• Professional subscriptions or training

Every pound or dollar you can deduct legally reduces your tax liability, so staying organised pays off—literally.

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Set Aside Money for Future Payments

If your income fluctuates, it’s wise to set aside a portion of each payment you receive (typically 25–30%) to cover taxes. This helps avoid scrambling for funds before each deadline. Consider opening a separate savings account specifically for tax payments so you’re always ready for quarterly deadlines.

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Make Your Payment on Time

The IRS accepts payments online via the IRS Direct Pay system or through your tax software. You can also mail a cheque with Form 1040-ES, but online payment is faster and includes instant confirmation. Paying by the September 16 deadline helps you stay in good standing and avoid penalties. Even if you’re behind, it’s better to pay something than nothing—partial payments reduce future interest and fees.

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Plan Ahead for the Rest of the Year

Once your September payment is handled, you’re three-quarters through the estimated tax year. Now’s the time to review your income projections, update your bookkeeping, and plan your final quarterly payment, which is due in January 2026. You can also use the Tax Refund Calculator to get an idea of where you stand and whether you’re likely to owe more—or get a refund—when you file your return.

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Staying ahead of the September tax deadline is crucial for self-employed individuals. By planning now, tracking expenses, and making an accurate payment, you’ll reduce your risk of penalties and keep your finances on track. A little preparation today makes tax season a lot less stressful tomorrow.