In this season, we can be sure of one thing. For FY S-corporations and partnerships that completed Form 7004 at the beginning of March, September 15 was the final deadline for forms 1120-S and 1065. If you have clients in this category, you are surely already thinking to yourself that missing a deadline is not such a big deal. It's just a matter of filing a couple of weeks late and paying, say, a penalty or two. However, the instinct of not thinking of missed deadlines makes such situations even worse.
The penalty isn't what most firms think it is
Ask 10 accountants about how the penalty for failing to file a partnership or an S corporation tax return works, and you will most likely get an explanation like the one that concerns the penalty for individual tax returns. Normally, the late-filing penalty for an individual tax return amounts to a certain percentage (up to 25%, depending on the amount owed tax). This is, however, not the case with S corporations and partnerships since they are pass-through entities and do not owe taxes at the entity level. Instead, Congress invented a different mechanism: the penalty is applied in the specified dollar amount multiplied by the number of shareholders or partners multiplied by the number of months (or their portions) that the return has not been filed up to 12 months.
For returns due in 2026 (including those that were due by September 15), the penalty rate is $255 for each shareholder or partner per month.
Let’s do the arithmetic for the client who has an S corporation with 4 shareholders filing its tax return 3 months later.
Therefore:
$255 × 4 shareholders × 3 months = $3,060
Note that this amount does not include interest, state penalty, or the penalty for K-1 form.
The penalty most firms forget stacks on top
Failure to file the return late doesn't just trigger the entity-level penalty. Every Schedule K-1 that goes out late or incomplete to a partner or shareholder carries its own separate penalty, currently around $330 per K-1 for 2026, rising sharply if the IRS decides the failure was intentional. That penalty stacks on top of the entity penalty - it doesn't replace it.
So, the real exposure to that same 4-shareholder S-corp, filed 3 months late with 4 late K-1s, isn't $3,060. It's closer to $4,380. Multiply that across a client roster where a handful of returns slipped, and you're looking at a number that's uncomfortable to explain in a client meeting.
The meter doesn't stop until you file - even if no one has noticed yet
Here's the interesting part: the IRS doesn't send notifications immediately. Some companies ignore missed deadlines thinking that as there has not been a notification yet, there must not be any crucial issues to worry about and go on dealing with other matters. But the penalties continue to accrue during this time - for each month the return is not filed, the number of penalties will keep on growing.
By the time the notification is received, a lot of time has already passed, and the penalties have gotten even bigger than expected. What prevents the penalties from accruing is filing of the return, not waiting for notification from the IRS. This is the most important message to get across to advisers who think that there is no urgency in situations when forms are not filed in time.
Two relief paths most firm’s underuse
This marks a change of circumstances in this story in a more positive situation. At the same time businesses forfeit opportunities to earn bonuses for their clients because the solutions are not a priority when time is pressing.
The First-Time Abatement (FTA) rule has been in place. Under this IRS rule entity free from tax history for the last three years can qualify for the abatement by simply requesting it from authorities with no need for any reasons or explanations for the abatement. It is administrative in nature rather than being a reasonable cause, which provides the chance to implement it much faster. However, many businesses do not even check their qualifications for this procedure and prefer applying adjudication route instead.
The same goes for small partnership relief. For partnerships comprising ten partners or fewer, it is easy to prove reasonable cause based on the traditional IRS statement for such cases in case the number of partners who have reported fully their share of income is proved.
Neither is automatic. Both require someone to build the request, track compliance history, and follow up - exactly the kind of work that gets deprioritized when a firm is already behind on filings.
The part that quietly compounds: state returns and the personal-return domino effect
Two more pieces rarely get their own line item in a firm's post-mortem:
State filings are processed on their own timeline. A company that has taken care of any federal taxes and presumes that the issue is finished could be caught off guard months later by a state notice regarding the same late filing. And since more clients are unknowingly surpassing state sales limits without realizing it, this complication is on the rise.
Late K-1s cause delays for the partners’ individual returns, as partners cannot file their Forms 1040 without obtaining a K-1. If the business files are late, the partner might find themselves rushing to submit their taxes by the second compliance deadline.
This week's work plan
· Act quickly and don't wait for notice. Obtain a list of all pass-through returns that were not filed on or before September 15, and file any that are ready right now without delay.
· Confirm FTA eligibility before you start preparing letters of reasonable cause. This is the quickest solution for many clients.
· Identify late personal returns today. If a K-1 is going to be issued late, make sure partners have filed their returns by October 15.
· List state liabilities separately. Do not assume that a federal solution means that everything has been fixed.
· Develop a compliance calendar to prevent this problem in the future. Firms that have made sure that their returns are not filed late do so because they have a system in place to flag high- risk returns 30-45 days in advance.
Where this tends to lead
For those organizations that notice they have "returns always coming in too late," "K-1s arriving late," or "a team that is always overloaded in a busy week," the issue is usually a capacity issue rather than an issue of skill. This indicates that there is insufficient manpower during busy season but no mechanisms in place to catch the problem before it escalates into a crisis.
Outsourced Tax Preparation is a solution to utilize "professionals trained in working in accordance with GAAP principles who can handle this situation at the busiest period of its operation." For those companies who want to retain their in-house operations, the alternative is to Hire Tax Preparation Staff or investigate Outsourced Accounting and Bookkeeping for a long-term solution.
Worth a look, too, if state exposure came up as a blind spot above: Multi-State Sales & Use Tax Compliance - a risk that's about to get a lot more relevant for any client selling across state lines this holiday season, as we cover here.
And since October is right around the corner - the natural point to clean up whatever tax season is left behind - it's worth reading why October is the best time to clean up your books before year-end deadlines start piling up too.
