October 15, 2026 Is the Extended Deadline for Your 2025 Federal Return. Here's the Sales Tax Question Your Accountant Probably Won't Ask
Form 4868 gave you six more months to file your 2025 federal tax return.
October 15, 2026 is the extended deadline for 2025 individual and C corporation federal tax returns. If you filed Form 4868 by April 15, you have 28 days left to finish. As the IRS stated in IR-2026-101, taxpayers who requested an extension to file their 2025 federal return should not wait until the October 15 deadline.
But here's what Form 4868 didn't give you — and what most accountants won't bring up while they're focused on finishing your income tax return.
It didn't give you extra time on your sales tax obligations. It didn't pause the accumulation of liability in states where you crossed a nexus threshold in 2025. And it didn't start the clock on voluntary disclosure — the mechanism that lets you resolve historical sales tax exposure before a state finds it first.
While you're pulling together your 2025 revenue data to finish your federal return, that same data answers one of the most important compliance questions your business may be facing. Here's what to look for.
What Form 4868 Actually Did — And Didn't Do
This distinction matters and the IRS is explicit about it.
As the IRS confirms, an extension provides extra time to file, not additional time to pay. Taxes owed for 2025 were due at the original April deadline. Interest and late-payment penalties have been running on any unpaid balance since April 15 — regardless of whether you filed Form 4868.
The same logic applies to sales tax — only more so. Sales tax obligations don't have an extension mechanism. If your business crossed an economic nexus threshold in Texas, Florida, or California in 2025 and didn't register, collect, and remit, that liability has been growing every month of 2026 — through April, through the extension period, and right now.
Form 4868 is irrelevant to all of it.
Do you already owe tax somewhere you’re not registered?
Two questions. No email required to see your answer.
Have your sales into any single state topped $100,000 in the last four quarters?
The Sales Tax Question Hiding in Your 2025 Revenue Data
Here's the thing about preparing your 2025 federal return — you're already doing the work that answers the nexus question.
To finish your return, you need your 2025 revenue by source, by state, and by channel. That's exactly the data you need to run a nexus analysis. The question is whether you ask the sales tax question while that data is already in front of you.
Economic nexus — the obligation to collect and remit sales tax in a state based on your sales activity there — triggers at $100,000 in annual sales in most states. Cross that threshold in 2025 and you had a collection obligation from the day you crossed it — not from when you registered, not from when you found out about it.
As your 2025 numbers come together, flag every state where you had more than $80,000 in sales. Those are the states where you may have crossed or approached the threshold. Check whether you're registered in each one. If you had more than $100,000 in a state where you're not registered — that's exposure worth addressing before it compounds further.
A few states use higher thresholds. California, Texas, and New York require $500,000 in annual sales before economic nexus triggers. For the remaining 40-plus states, $100,000 is the line.
For the complete 2026 state-by-state threshold breakdown, read our complete economic nexus guide.
The Marketplace Trap — Why Amazon Sellers Need to Check This Too
If you sell through Amazon, Etsy, or another marketplace facilitator, you may be thinking you're covered — the platform collects and remits sales tax on your behalf in most states.
That's true for marketplace transactions. But in most states, those marketplace sales still count toward your economic nexus threshold for your direct sales. As UltraCart's 2026 nexus guide explains, you can cross a state's threshold on the strength of your Amazon volume, owe a registration in that state for your direct sales, and never realize it because the marketplace was quietly handling its own collection the whole time.
Your 2025 nexus analysis needs to look at marketplace sales and direct sales combined — not just your Shopify or website numbers.
Why October Is the Best Month of the Year to Do This
The timing of this analysis matters more than most people realize.
Most states' voluntary disclosure programs — the mechanism for resolving historical sales tax exposure proactively — use a lookback period of two to four years. That lookback typically covers 2022, 2023, 2024, and 2025 for businesses coming forward today.
If you had uncollected sales tax obligations in 2025 and address them now through a voluntary disclosure agreement, the liability is limited to that lookback window. Penalties are typically waived or significantly reduced. And the process happens on your terms — not the state's.
If a state finds you first — through AI-powered audit selection, marketplace facilitator data matching, or a routine nexus review — the lookback period can extend further, penalties apply in full, and the process happens on the state's timeline.
October is the best month to do this analysis because your 2025 numbers are complete, your books are being finalized for your tax return, and the voluntary disclosure window is wide open. By January, your 2026 numbers start adding another year of exposure on top of whatever 2025 created.
The SALT Connection — One More Reason Your 2025 Return Matters for Sales Tax
While your accountant is working on your 2025 return, there's one more sales tax angle worth flagging.
The One Big Beautiful Bill raised the SALT deduction cap from $10,000 to $40,000 for taxpayers making $500,000 or less in modified adjusted gross income for 2025. That means for your 2025 return, you may be able to deduct significantly more in state and local taxes — including state and local sales taxes you paid on major purchases — than in any prior year since 2017.
If you're in a no-income-tax state — Texas, Florida, Washington, Nevada, Tennessee — and you made significant purchases in 2025, the sales tax deduction may be worth calculating alongside or instead of the income tax deduction. A new car, major equipment, a significant home renovation — all of these carry sales tax that may now be fully deductible under the expanded cap.
We covered the full SALT deduction angle in our One Big Beautiful Bill article.
What to Do Before October 15
Three things worth doing in the next 28 days — while your 2025 numbers are already in front of you.
First, run the nexus check. Pull your 2025 revenue by ship-to state across every channel — marketplace, direct, wholesale. Flag every state above $80,000. Verify your registration status in each one.
Second, if you find exposure, assess your voluntary disclosure options. Most states have VDA programs that limit the lookback period and waive penalties. Coming forward now is dramatically less expensive than being found later.
Third, if you're in a no-income-tax state and made major purchases in 2025, flag the SALT deduction conversation with your accountant. The $40,000 cap under the One Big Beautiful Bill may change your deduction strategy for your 2025 return.
The October 15 deadline is in 28 days. Your 2025 data is already being pulled together. The sales tax question is worth asking while you're already in the numbers.
Not sure whether your 2025 revenue crossed a sales tax nexus threshold — or want to understand your voluntary disclosure options before October 15? Book a free consultation with our team at sales.tax. We'll run a nexus analysis on your 2025 numbers and help you understand exactly where you stand before the extended deadline passes
What this means for your business
Thresholds move, rules change, and nobody tells you when you cross one. We’ll tell you where you stand in 30 minutes — and if there’s nothing to fix, we’ll say so.