S corp and partnership return errors
The extended deadline for calendar-year S corporation and partnership returns was September 15. The owners' personal returns were due October 15. If your business return went in during the last week, under pressure, it's worth a second look now.
Mistakes on these returns rarely show up right away. They come months later as a penalty notice, a K-1 mismatch letter, or an audit question. Clients ask me what to check for S corp and partnership return errors. Here are the six things I'd look at first, and how each gets fixed.
Why a rushed business return comes back later
An S corporation or partnership usually pays no income tax itself. Income passes to the owners on Schedule K-1. So the IRS needs the business return on time, complete, and consistent with every owner's return. When one of those breaks, the problem lands on the business, the owners, or both.
1. A late 1120-S penalty, or the extension didn't count
A late Form 1120-S or Form 1065 carries a flat penalty that has nothing to do with tax owed. For 2025 returns filed in 2026, it's $255 per owner, per month or part of a month, for up to 12 months. Count everyone who was an owner at any time during the year. The rules are in sections 6698 (partnerships) and 6699 (S corporations). I explained the math in Why a late S-corp return gets a penalty even when no tax is due.
The midnight filing that cost $12,240
This happened to a client of mine. It was September 14, less than 24 hours before the extended deadline. A growing consulting firm with eight owners was in chaos. The bookkeeper was chasing the owners for missing receipts while the managing owner rushed to finish the S corporation's Form 1120-S.
They hit submit before midnight and relaxed, sure they were filing on extension.
Six months later an IRS penalty notice arrived. In the rush, nobody had noticed that the Form 7004 extension was never filed back in March. Without that extension, the IRS treated the September return as six months late.
The company owed zero income tax. It didn't matter. Under Section 6699 the penalty is a flat $255 per owner, per month: 8 owners times 6 months, $12,240.
The first thing I check in a case like this is first-time abatement. If the company filed on time the prior three years with no penalties, the IRS will often take it off.
Two things people miss:
An extension has to be filed by the original due date (March 16, 2026 for calendar-year 2025 returns). If Form 7004 never went in, or went in late, the September filing was late too.
An incomplete return can be penalized like a late one. Leaving off required information can trigger the same per-owner penalty.
If you get the notice, look at relief before you pay:
First-time abatement. If the business filed the same return on time for the prior three years with no penalties, the IRS will often remove a late-filing penalty. Under the IRS manual, it doesn't cover the penalty for an incomplete partnership return.
Rev. Proc. 84-35. A partnership is presumed to have reasonable cause if it has 10 or fewer partners, all individuals (not nonresident aliens) or estates of deceased partners, every item is split the same way, and every partner reported their share on a timely personal return. A married couple filing jointly counts as one partner.
Reasonable cause. Something outside your control, like a serious illness or a disaster, with records to back it up.
2. K-1 errors: the K-1s don't tie out
Each K-1 has to add up to the totals on the return, and each owner's personal return has to report what the K-1 says. The law requires owners to treat items consistently with the business return. An owner who disagrees has to say so on Form 8082. Otherwise the IRS can simply adjust the owner's return to match.
Common rush errors:
K-1s issued from a draft, then the return changed before filing
An owner who joined or left mid-year, with the wrong percentage or dates
In an S corp, income split some way other than by shares owned. S corps can't do special allocations. Income follows stock ownership, day by day.
In a partnership, allocations that don't follow the partnership agreement, or guaranteed payments to a partner reported in the wrong box
3. S corp basis and Form 7203 were never tracked
Basis decides whether an S corp owner can deduct a loss and whether a distribution is tax-free. A loss larger than your stock and loan basis isn't deductible that year. It carries forward. A distribution larger than your stock basis is generally taxed as a gain.
Since 2021 returns, a shareholder must attach Form 7203 to the 1040 if they claim an S corp loss, receive a non-dividend distribution, sell or otherwise dispose of stock, or get a loan repaid by the corporation. If you filed your 1040 by October 15 without it, and you needed it, that's a fixable gap. Rebuilding basis takes every prior year's K-1, so start now.
The personal guarantee trap.
Can you imagine partnering in a business only to take the risk, without receiving any gains? That's how a lot of S corp owners feel when they learn this rule.
Several accountants have asked me the same question lately. Their client didn't put his own money into the S corp. He personally guaranteed a bank loan, and the bank paid the money to the company directly. Does that give him basis?
Short answer, no. Not by itself. The S corp regulations say it plainly: a shareholder doesn't get debt basis just by guaranteeing a loan (Treas. Reg. 1.1366-2(a)(2)(ii)). Debt basis only comes from a bona fide loan that runs directly from the shareholder to the corporation. Once you actually pay on the guarantee, you get basis for what you paid. Tax Court cases like Phillips (T.C. Memo. 2017-61) have held to that, even with more than $100 million in judgments against the shareholder and her co-guarantors. She never paid, so there was no basis.
A partnership works differently. When a partner personally guarantees a partnership loan, that partner generally bears the economic risk of loss for the debt, so the debt is allocated to that partner as a recourse liability (Treas. Reg. 1.752-2). Under IRC 752, an increase in a partner's share of partnership debt is treated as if the partner put in money, so it adds to the partner's basis, even though they haven't paid a dime. Same guarantee, same bank, and a completely different result depending on which type of entity you picked. (The at-risk and passive activity rules can still limit the losses, and some guarantees, like "bottom dollar" guarantees, don't count.)
If an S corp owner wants basis, the money has to come out of his pocket. Either he borrows it personally and then lends it or contributes it to the company, or he pays on the guarantee. If the losses were already taken based on a guarantee, expect the IRS to come back for them.
4. Schedules K-2 and K-3 were left off
These schedules report international tax information. Many S corps and partnerships with no foreign activity can skip them under the "domestic filing exception." For 2025, the main conditions are:
No foreign activity, or only a small amount of passive foreign income
For partnerships, every direct partner is a U.S. citizen, a resident alien, or one of certain domestic estates, trusts and entities
The owners were told, no later than when they got their K-1s, that they'd only get a K-3 if they asked
No owner asked for one by one month before the return was filed
If the business didn't meet those conditions and left the schedules off, the return may be treated as incomplete. That brings back the per-owner penalty from point 1.
5. No partnership representative, or a missed election out
Under the partnership audit rules in effect since 2018, every partnership has to name a partnership representative on its return, unless it elects out. That person has sole authority to deal with the IRS in an audit, and their decisions bind the partnership and every partner. If the partnership doesn't name anyone, the IRS can choose.
Smaller partnerships can often elect out on Schedule B-2. It requires 100 or fewer eligible partners, and no partner can be another partnership, a trust, or a single-member LLC. The election only counts on a timely filed return. If it was missed on the 2025 return, it can't be added now. Put it on the 2026 checklist.
6. The owner's salary
If you work in your S corp and take distributions, the IRS expects a reasonable salary run through payroll. A rush filing doesn't create this problem, but it often hides it. I covered how the IRS handles it in Audited over a low S corp salary while your friend wasn't?
How to fix S corp and partnership return errors after the deadline
The right fix depends on the type of entity:
S corporation: file an amended Form 1120-S (check the amended return box) with a statement explaining each change, plus amended K-1s. Owners whose numbers changed generally file Form 1040-X.
Partnership under the audit rules (most partnerships): a corrected return filed by September 15, under a valid extension, would generally have replaced the first one. After the deadline, the partnership generally can't amend or send amended K-1s. It files an administrative adjustment request (AAR). The adjustment usually flows to partners in the current year, or the partnership pays at the entity level. It does not work like a normal amendment.
Partnership that validly elected out: it can file an amended Form 1065 with amended K-1s, and partners amend their own returns.
The S election itself wasn't in place: if you filed as an S corp but the IRS never accepted the election, late election relief under Rev. Proc. 2013-30 often applies, generally within 3 years and 75 days of when you wanted the election to start.
An amended return isn't automatic. The IRS has discretion over how it handles one, so file it right the first time. See Is the IRS forced to accept an amended tax return? No.
Most taxpayers don't realize when they need an accountant's advice. In most cases, clients ask me after the fact, when the major negative tax consequences have already happened. The time to ask about a guarantee, a new partner, or an entity choice is before you sign.
FAQ
What is the penalty for filing a late 1120-S or 1065?
For 2025 returns filed in 2026, $255 per owner, per month or part of a month, for up to 12 months, even if no tax is due. First-time abatement or reasonable cause may remove it.
How do I fix a mistake on a filed 1120-S?
File an amended Form 1120-S with the amended return box checked, a statement explaining each change, and amended K-1s. Owners whose numbers changed generally file Form 1040-X.
Can my partnership just send out corrected K-1s?
Usually not after the deadline. Most partnerships have to use an administrative adjustment request (AAR) instead.
Do I need to attach Form 7203?
Yes, if you claim an S corp loss, receive a non-dividend distribution, sell or dispose of stock, or get a loan repaid by the corporation.
Does guaranteeing my S corp's bank loan give me basis?
No, not by itself. You get debt basis only for money you lend the corporation directly or for what you actually pay on the guarantee. A partner's guarantee of a partnership loan generally does add to that partner's basis.
Related: Why a late S corp return gets a penalty even when no tax is due · Audited over a low S corp salary? · Is the IRS forced to accept an amended return?
Official sources: IRS: About Form 1120-S · IRS: About Form 7203 · IRS: BBA centralized partnership audit regime
Filed an S corp or partnership return in a rush?
We'll go through the return, the K-1s, and any notice you've received, and I'll tell you honestly what I see. I help with S corp and partnership returns and tax problems with the IRS, New York, New Jersey, Connecticut and Pennsylvania.
Solomon Grosinger, Enrolled Agent
I'm licensed by the IRS and have represented taxpayers before the IRS and New York, New Jersey, Connecticut and Pennsylvania tax agencies from Brooklyn since 2017.
General info, not advice for your specific case.
