September 15, 2026: Q3 estimated taxes (and a few entity due dates) on the same day
September 15, 2026 is the IRS due date for the third 2026 estimated tax payment for individuals (Form 1040-ES). For calendar-year taxpayers, that installment is the one that usually covers income from June through August. It is also, separately, the extended filing date for calendar-year partnerships (Form 1065) and S corporations (Form 1120-S) that filed a timely Form 7004.
If you are self-employed, you sold a business or a block of stock, you vested a large RSU tranche, or your 1099 income jumped, the April and June payments you already made may be too small. Underpayment penalties are not huge compared with the tax itself, but they are avoidable.
Picnic Tax is a CPA marketplace, not an IRS payment processor. You still pay the Treasury via Direct Pay, EFTPS, IRS Direct Pay, a credit-card processor, or the 1040-ES voucher. What Picnic sells is a tax planning and advice job (from about $300) so the number you send on September 15 is based on your year-to-date income, withholding, and safe-harbor math — or a filing job if what you actually need is the extended 1065 / 1120-S / 1040 itself.
Who this is for
- Freelancers, partners, and LLC members who pay 1040-ES four times a year.
- W-2 employees with side income, RSUs, or a big capital gain whose withholding will not cover 2026 tax.
- Calendar-year S corps and partnerships that extended and still need the return filed by September 15, 2026 (that is a filing deadline, not an estimate).
- People who want a CPA to run annualized-income method math after a lumpy summer.
Who this is not for
- Employees whose only income is a W-2 with enough withholding. You generally are not required to make estimated payments.
- Anyone who thinks paying Picnic is paying the IRS. It is not. Two different payments.
- Households under the “no penalty if you owe under $1,000” threshold who do not need a $300 planning session to send $0.
- Simple “send 25% of last year’s tax” cases you can do from last year’s Form 1040, line for total tax. Safe harbor is often enough without a CPA.
Honest explainer: three different September 15 jobs
| If this is you | What is due September 15, 2026 | Picnic product |
|---|---|---|
| Self-employed / investor who pays estimates | Q3 2026 1040-ES payment (2026 tax year) | Planning, from about $300 |
| W-2 + large RSU vest or sale this summer | Same Q3 estimate, or extra withholding on a later paycheck if still possible | Planning, from about $300; equity is a named Picnic service |
| Calendar-year S corp or partnership that extended | File 1120-S or 1065 (and often K-1s to owners) | Small-business filing, from about $750 |
| Individual who extended the 2025 1040 | Nothing about the 2025 return is due Sep 15; that return is due October 15, 2026 | Don’t mix the years. See the tax extension help page |
| C corp estimates | Corporate estimated-tax rules differ (generally 25% of required annual payment; $500+ threshold) | Ask in onboarding; do not use 1040-ES rules by analogy |
How much to pay (federal individual, high level)
The IRS underpayment penalty generally looks at whether you paid in enough throughout the year, not only whether you settle up next April. Common safe harbors (confirm current-year Form 1040-ES and Pub 505):
- Pay at least 90% of this year’s tax, or
- 100% of last year’s tax (generally 110% if your prior-year AGI exceeded the high-income threshold, commonly $150,000 MFJ / $75,000 others — confirm the current 1040-ES).
If income is lumpy, the annualized income installment method can lower the required Q3 payment. That is worksheet work. It is a reason to hire a CPA instead of dividing last year by four.
State estimates (California, New York, etc.) have their own dates and percentages. Some states do not match September 15.
Price ranges (Picnic)
- Tax planning and advice (estimated payment, annualized method, RSU withholding gap): from about $300.
- Personal 2025 return (if you are also behind on last year): from about $225–$250 + $50 per extra state. Different tax year than the 2026 estimate.
- Small-business entity filing: from about $750.
- Quote from the questionnaire. Stripe. Payment held until you accept the work. CPA pays Picnic’s commission.
A $300 planning job that prevents a penalty and a cash crunch is the usual September purchase. Do not buy a full 1040 in September unless you also need last year’s return done.
Get a CPA to size the payment
Get a CPA to size the September 15 payment: picnictax.com
Or run a rough federal number first with the Q3 estimated tax calculator — an estimate only, not advice and not a filing.
Pay the IRS separately through IRS Direct Pay or EFTPS after you have the number.
FAQs
What period does the September 15, 2026 payment cover?
For most calendar-year individuals, the third installment toward 2026 tax, typically associated with income from June through August. It is not a payment on your 2025 return.
Can I skip Q3 if I will get a refund next April?
If withholding plus prior estimates already clear a safe harbor, you may not need this installment. If you skip it because you “feel” fine, and you turn out to owe, the penalty is calculated by quarter. Run the numbers.
Does Picnic send the money to the IRS?
No. Picnic pays the CPA (after you accept the work). You pay the IRS yourself. Keep the confirmation.
I have a huge RSU vest in July. Is 22% withholding enough?
Often not, if your marginal rate is 32–37% plus state. The gap shows up as an estimate (or a large April bill). Picnic’s equity compensation service exists for this; a planning session can translate vest FMV into a Q3 payment. The RSU tax gap calculator is a starting estimate, not advice.
My S corp extended. Is September 15 a payment date or a filing date?
For the entity return, it is the filing date. Owners may also have a personal estimated payment the same day. Those are two different tickets.
What if September 15 falls on a weekend?
In 2026, September 15 is a Tuesday, so the listed IRS date stands. (If a future year lands on a weekend or legal holiday, IRS rules push to the next business day.)
This page is general information, not tax advice. Picnic Tax matches you with an independent U.S. CPA. Using this page does not create a client relationship. Paying Picnic is not paying the IRS.