Q3 Estimated Taxes Are Due September 15: What Individuals, Businesses, and Nonprofits Need to Know

If you don't have taxes withheld from a regular paycheck, the IRS expects you to pay your taxes in installments throughout the year rather than in one lump sum the following April. The third installment of the 2026 tax year is due September 15, 2026. It applies to a wider group of people than most expect, including self-employed individuals, small business owners, corporations, and even nonprofits with certain types of income. This post breaks down, in plain terms, who this deadline applies to, why it exists, and what to do before it arrives.

Why Estimated Taxes Exist

The U.S. tax system is a pay-as-you-go system. Employees meet this requirement through payroll withholding. Anyone whose income isn't subject to withholding, such as freelancers, business owners, investors, and certain organizations, is expected to estimate their tax liability and pay it in installments throughout the year, according to IRS guidance on estimated taxes. The 2026 due dates fall in April, June, September, and the following January, with the third installment landing on September 15, 2026.

Example:  Maria is a freelance graphic designer in Trenton. No employer withholds tax from her income, so she must estimate and pay her own tax four times a year. If she skips her September payment and tries to settle everything at once next April, she is likely to owe a penalty on the amount she should have paid by September 15, even if her final return shows a refund.

For Individuals: Do You Owe a Q3 Payment?

You generally need to make estimated payments if you expect to owe at least $1,000 in tax for the year after subtracting withholding and refundable credits. This commonly applies to:

• Sole proprietors, freelancers, and independent contractors

• Partners in a partnership and S corporation shareholders

• Individuals with significant investment, rental, or self-employment income

The IRS offers a safe harbor. If you pay at least 90% of the current year's tax liability, or 100% of last year's liability (110% if your prior year adjusted gross income was above $150,000), spread evenly across the four due dates, you generally avoid an underpayment penalty even if you owe more when you file.

Example:  David is a self-employed consultant whose income grew significantly in 2026 compared to 2025. Rather than trying to calculate his exact 2026 liability mid-year, he pays 110% of what he owed in 2025 in four equal installments because his 2025 adjusted gross income was above $150,000. Because he met the safe harbor, he will not owe an underpayment penalty for 2026, even though his final bill next April will be larger than what he paid in installments.

For Businesses: Corporate and Small Business Obligations

Corporations deposit their third installment of 2026 estimated tax by the same date, per the IRS quarterly tax calendar, generally through the Electronic Federal Tax Payment System (EFTPS). Owners of pass-through entities, such as LLCs, partnerships, and S corporations, typically pay at the individual level instead, based on their share of business income.

Example:  A small landscaping company organized as an LLC does not pay federal income tax at the entity level. Instead, its two owners each report their share of the company's profit on their personal returns and make their own quarterly estimated payments based on that share.

For New Jersey-based businesses, don't forget the state side. New Jersey has its own estimated tax filing requirements and due dates, tracked on the NJ Division of Taxation's tax calendar and following the same quarterly schedule as the federal one. Business owners who only plan around the federal deadline sometimes miss the state payment, which carries its own penalty structure.

For Nonprofits: When Tax-Exempt Doesn't Mean Tax-Free

Tax-exempt status covers revenue tied to your organization's mission, such as donations, grants, and program income. It does not automatically cover everything an organization earns. Income from a regularly carried on trade or business that isn't substantially related to your exempt purpose can be classified as Unrelated Business Taxable Income (UBTI), and organizations with UBTI are expected to make quarterly estimated tax deposits, including one due September 15, 2026, per the IRS's exempt organization guidance.

Example:  A community theater nonprofit owns a small parking lot next to its building. On weekdays, when there are no performances, it rents the lot to a nearby office for employee parking. Because that rental activity is regularly carried on and isn't related to the theater's mission of staging performances, the income it generates can be classified as UBTI, and the organization may owe quarterly estimated tax on it, separate from its Form 990 filing.

This is separate from your annual Form 990 filing, which is due the 15th day of the 5th month after your fiscal year ends (May 15 for calendar year organizations, per the IRS). A nonprofit can be fully compliant on its 990 and still owe quarterly estimated tax on UBTI if it has taxable unrelated income. Boards and finance committees are well served by reviewing, at least once a year, whether any revenue stream might fall into this category.

Three Steps to Take Before September 15

• Reconcile your books through the current quarter so your income and expense figures are accurate. An estimate is only as good as the data behind it.

• Compare year-to-date income against your prior year figures to decide whether the safe harbor percentage (90% of this year, or 100 to 110% of last year) makes more sense for your situation.

• Check both federal and New Jersey state due dates. They don't always require the same payment method, and penalties are calculated separately.

The Bottom Line

September 15 is a real deadline with a real penalty for missing it, but it's also predictable. Organizations and individuals who handle it smoothly almost always have clean, current books and a clear picture of their year-to-date income well before the date arrives. That's the groundwork bookkeeping, accounting, and fractional CFO support are built to provide: not just compliance, but the clarity to make the payment with confidence instead of guesswork.

Parks Projects NJ provides bookkeeping, accounting, tax preparation, and fractional CFO services for individuals, businesses, and nonprofits. If you have questions about how the September 15 deadline applies to your specific situation, reach out. We're glad to help you work through it.

Sources: Internal Revenue Service (irs.gov): estimated tax FAQs, third quarter tax calendar, and exempt organization filing guidance. New Jersey Division of Taxation (nj.gov): estimated tax and due date guidance. This article is educational and general in nature and is not individual tax advice.