Can I file my taxes without a K-1 and amend later?

You can, but it usually costs more than extending. The partnership files a copy of your K-1 with the IRS, so leaving it off means a Form 1040-X later with interest from April 15, 2027, and possibly a notice first. Filing Form 4868 and paying an estimate gets the same result without a second return.

Does filing an extension for a late K-1 raise my audit risk?

No. Form 4868 is automatic and the IRS processes millions of them a year. What draws attention is a return whose K-1 numbers don't match the K-1 the partnership filed, which is a reason to wait for the real form rather than rush.

What is the latest a partnership can send my K-1?

For a calendar-year partnership that files Form 7004, September 15, 2027 for the 2026 tax year. IRC §6031(b) requires the K-1 by the partnership's due date including extensions. That leaves you one month before your own extended deadline of October 15, 2027.

What if my K-1 still hasn't arrived by October 15?

File anyway. Treas. Reg. §1.6081-4 gives one automatic six-month extension and there is no second one for a domestic filer. Report your best estimate of the K-1 and attach Form 8082, then amend if the real K-1 differs.

The Journal / Business Tax

Waiting on a K-1 to File Taxes? Extend, but Pay 90% by April 15.

By Ewan Morkel, EAOctober 16, 20266 min read

A partnership that extends its own return can send your K-1 as late as September 15, 2027. File Form 4868, but send an April payment built from last year's K-1, because the extension does nothing for the tax itself.

Hands opening a brown envelope with a white sheet of paper over a wooden table

An investor with a 20% stake in a friend's HVAC company has everything for the 2026 return by mid-March except one form. The company's accountant files an extension, and the Schedule K-1 shows up in mid-September. If you're waiting on a K-1 to file taxes, that timeline is normal. Nothing went wrong. The business is allowed to be that late, and your return is still due April 15, 2027.

The timeline

Why you're waiting on a K-1 to file taxes at all.

Partnership returns (Form 1065) and S corporation returns (Form 1120-S) for calendar 2026 are due March 15, 2027 under IRC §6072(b), a month before yours. Form 7004 extends them six months, to September 15, 2027. The K-1 rides along: IRC §6031(b) gives a partnership until its due date, extensions included, to get you the form, and §6037(b) has an S corporation furnish it by the day it files. So the business can legally hand you a K-1 one month before your own extended deadline.

Investment funds and real estate syndications are the usual late senders, since many of them own other partnerships and can't finish until those K-1s arrive. A small operating business is late for a plainer reason: the books aren't closed. Either way, the delay is outside your control, and the April payment is not.

The trap

The extension covers the paperwork, not the tax.

Form 4868 is automatic. Nobody approves it and you don't need a reason. What it doesn't move is the payment date. Tax unpaid on April 15 picks up the failure-to-pay penalty of 0.5% a month under §6651(a)(2), plus interest, which is 7% for the fourth quarter of 2026 under Rev. Rul. 2026-15 and resets quarterly. Skip the extension entirely and the failure-to-file penalty under §6651(a)(1) runs 5% a month, which is what a missed extension deadline actually costs.

The second trap is the estimate line on Form 4868 itself. In Crocker v. Commissioner, 92 T.C. 899 (1989), the Tax Court held that an extension is void when the taxpayer doesn't make a proper estimate of the tax, and the IRS can decide that after the return comes in. A low estimate made in good faith survives. Typing zero because the K-1 hasn't come, when last year's K-1 showed $60,000, is the cleanest way I know to lose the extension and get the 5% a month anyway.

One investor, real numbers

Building the April payment from last year's K-1.

Back to the HVAC investor. Married filing jointly, $230,000 of combined W-2 wages with $33,000 of federal withholding, and a 2025 K-1 showing $60,000 of ordinary business income. As an investor who doesn't work in the business, that income is passive: no self-employment tax, but it counts toward the 3.8% net investment income tax under §1411 once modified AGI passes $250,000. It also gets the 20% qualified business income deduction under §199A, since taxable income sits far below the $403,500 joint threshold for 2026.

Run last year's K-1 through this year's brackets and it adds $12,768 of federal tax. Round up, send $12,800 with the extension, and stop thinking about it until September.

Waiting on a K-1, married filing jointly, 2026 return

Combined W-2 wages: $230,000
Federal withholding: $33,000
2025 K-1 income, used as the estimate: $60,000
Estimated tax on it (22% and 24% brackets, plus NIIT): $12,768
Paid with Form 4868 by April 15, 2027: $12,800
Actual 2026 K-1, received September 14, 2027: $75,000
Actual 2026 federal tax, including $2,090 of NIIT: $49,158
90% of actual tax: $44,242
Paid by April 15 ($33,000 + $12,800): $45,800
Late-payment penalty: $0
Interest on the $3,358 balance, paid September 30: $108

Tax year 2026, federal only. Joint brackets and the $32,200 standard deduction from Rev. Proc. 2025-32. K-1 income is passive trade or business income, eligible for the 20% §199A deduction, with the 3.8% §1411 tax on the lesser of that income or the amount by which modified AGI exceeds $250,000. Interest is simple interest at 7% for the 168 days from April 15 to September 30, 2027, assuming the Rev. Rul. 2026-15 rate holds; the IRS compounds daily and resets the rate each quarter. Ignores state tax and any §6654 estimated tax penalty.

The K-1 came in $15,000 higher than last year and the April payment still cleared the 90% line with $1,558 to spare. Now run the same year two other ways. Extension filed, nothing paid in April: $485 of failure-to-pay penalty on the $16,158 balance plus about $521 of interest, $1,006. No extension, return filed September 30: a $3,636 failure-to-file penalty (4.5% a month for five months, after the §6651(c)(1) offset), plus the same $485 and $521, for $4,642. Same K-1, same tax, and a $4,534 spread decided entirely in April.

What I'd do

When the estimate is a guess, guess high.

If last year's K-1 is the only data you have, pay on it plus a cushion, and ask the business for a number. Many funds send K-1 estimates in March or early April, and a small company's accountant can usually give you a range once the books are mostly closed. Overpaying costs you nothing; the excess comes back as a refund or rolls into 2027 estimates. Falling below 90% costs 0.5% a month on the entire unpaid balance, not just the shortfall.

Don't file in April without the K-1 and plan to amend. The partnership sends the IRS a copy of every K-1 it issues, so a return that leaves one off gets corrected for you, with interest. If October 15 comes and the K-1 still hasn't, file on your best estimate and attach Form 8082, which the instructions call for when a K-1 didn't arrive by the due date including extensions. Reporting differently from the partnership without that notice invites the 20% accuracy penalty of §6662 under the consistency rule of §6222, or §6037(c) for an S corporation.

Two other deadlines care about this K-1. The extension does nothing for the §6654 underpayment penalty, which is measured quarter by quarter; with 2025 AGI over $150,000, withholding has to reach 110% of last year's tax to be safe, and the safe harbor calculator gives you that number. And Utah extends your state return automatically with no form, but only if by April 15 you've prepaid 90% of your 2026 Utah tax or 100% of your 2025 Utah tax. When the K-1 is the unknown, last year's number is the test you can actually measure.