Business Entities · Corporations in general

Filing requirements, due dates, and penalties

Corporate filing is mostly mechanical, and the mechanics have one moving part this year. A transitional rule that has kept June-year-end C corporations on an earlier filing date for a decade expires with the taxable year beginning 1 July 2026, so the same corporation files on one date for the year ending 30 June 2026 and on a different one for the year ending 30 June 2027. Almost everything else on this page has been stable for years, which is precisely why the one change is worth being exact about.

The rule

When the return is due. the 15th day of April following the close of a calendar year, or the 15th day of the fourth month following the close of a fiscal year — a C corporation falls under the general rule in IRC § 6072(a), not the third-month rule in § 6072(b) that governs partnerships and S corporations^TY2026

Except for a June year end, until now. a C corporation with a taxable year ending 30 June filed on the 15th day of the third month after the close — 15 September for a June year — rather than the fourth. That deferral came from Pub. L. 114-41 § 2006(a)(3)(B), which applied the new dates to such a corporation only for returns for taxable years beginning after 31 December 2025. The year beginning 1 July 2025 and ending 30 June 2026 is the last one under the old date; the year beginning 1 July 2026 is the first under the general fourth-month rule^TY2026

Extension. a corporation, or an affiliated group filing a consolidated return, is allowed an automatic 6-month extension of time to file where an application is submitted on Form 7004 on or before the date prescribed for filing, the properly estimated unpaid tax liability is remitted on or before the date prescribed for payment, and the application lists each member of any affiliated group. The extension is of time to file only, not of time to pay (Reg. § 1.6081-3(a), (b))^TY2026

And its own June exception. for a return for a taxable year of a C corporation that ends on 30 June and begins before 1 January 2026, the automatic extension is 7 months rather than 6, a short period ending on any day in June being treated as ending on 30 June. That exception expires with the same year as the filing-date deferral, so a June year beginning 1 July 2026 gets 6 months like any other corporation (Reg. § 1.6081-3(e))^TY2026

Failure to file. 5 percent of the tax required to be shown on the return for a failure of not more than 1 month, with an additional 5 percent for each additional month or fraction of one during which the failure continues, not exceeding 25 percent in the aggregate — measured from the date prescribed determined with regard to any extension, and not applying where the failure is due to reasonable cause and not wilful neglect (IRC § 6651(a)(1))^TY2026

Failure to pay. 0.5 percent of the tax shown on the return for a failure of not more than 1 month, with an additional 0.5 percent for each additional month or fraction of one, subject to the statutory ceiling — measured from the date prescribed for payment determined with regard to any extension of time for payment, and not applying where the failure is due to reasonable cause and not wilful neglect (IRC § 6651(a)(2))^TY2026

How they interact. for any month to which both additions apply, the failure to file addition is reduced by the amount of the failure to pay addition — so the two do not simply accumulate, and the combined charge for a month in which both run is the higher rate rather than the sum (IRC § 6651(c)(1))^TY2026

The floor for a return more than sixty days late. $535 — for a return required to be filed in 2027, the IRC § 6651(a) addition to tax for failure to file an income tax return within 60 days of the due date, determined with regard to extensions, will not be less than the lesser of that amount or 100 percent of the amount required to be shown as tax on the return^TY2026

Electronic filing. a corporation must file Form 1120 electronically if it is required to file at least 10 returns during the calendar year ending with or within its taxable year, and every member of a controlled group must do so where the group's aggregate is at least 10 — with no asset threshold (Reg. § 301.6011-5(a))^TY2026

Current figures

How it works in practice

Get the entity type right before the date. A C corporation files under the general rule in IRC § 6072(a) — the fifteenth day of the fourth month after the close of the year. Partnerships and S corporations file under IRC § 6072(b), the fifteenth day of the third month. The two are a month apart in the opposite direction from what most people remember, because the pass-through entities file first: their owners need the Schedules K-1 before their own returns are due.

The June exception is the item to be careful with in 2026 and 2027. When the filing dates were rewritten in 2015, C corporations moved from the third month to the fourth — but a corporation with a June year end was left on the old date for a further decade. That deferral applies to returns for taxable years beginning before 1 January 2026, so the last year covered is the one beginning 1 July 2025 and ending 30 June 2026, due 15 September 2026. The next year, beginning 1 July 2026, is on the general rule and is due 15 October 2027.

The extension carries the same split and expires with it. A corporation gets an automatic six-month extension on a timely Form 7004 with the estimated unpaid liability remitted; a June-year C corporation whose year begins before 1 January 2026 gets seven months instead. Both halves of the June concession end together, so the year ending 30 June 2027 gets the ordinary six months from the ordinary fourth-month date.

Two things about the extension are worth stating because they are so often assumed away. It is an extension of time to file, not to pay (Reg. § 1.6081-3(b)), and the failure-to-pay addition runs from the unextended payment date regardless. And it is conditional: remitting the properly estimated unpaid tax liability is one of the requirements, so an application filed without payment is vulnerable.

On penalties, the two additions in IRC § 6651(a) are different animals. Failure to file is charged on the tax required to be shown on the return, at five percent a month to a twenty-five percent ceiling. Failure to pay is charged on the tax shown, at half a percent a month. Both count a fraction of a month as a whole month, and both measure from a date determined with regard to any extension — but they are different extensions: the filing date for the first, the payment date for the second.

IRC § 6651(c)(1) is the provision that stops the two accumulating and is routinely overlooked. For any month to which both apply, the failure-to-file addition is reduced by the failure-to-pay addition. So a corporation both late in filing and late in paying is charged at the higher rate for those months, not at the sum of the two.

The minimum addition applies where a return is more than sixty days late, and it is the lesser of a fixed indexed amount or the whole of the tax required to be shown. It is indexed annually, so the figure has to come from the revenue procedure rather than from IRC § 6651(a) itself.

Scenarios

How this has changed

The filing dates were rewritten in 2015 and the change was a swap. Before it, C corporations filed in the third month and partnerships in the fourth; afterwards, partnerships and S corporations file in the third month and C corporations in the fourth. The purpose was to let the pass-through entities report to their owners before the owners’ own returns were due, and it reversed the order that had held for decades. Any material describing a March date for a C corporation is pre-2016 — and, awkwardly, is correct for a June year end in every year before the one now beginning.

The June concession is the residue of that swap. Pub. L. 114-41 § 2006(a)(3)(B) gave C corporations with a June year end an extra ten years on the old date, and Reg. § 1.6081-3(e) gave them a seven-month extension to match. Both are drafted by reference to taxable years beginning before 1 January 2026, so both expire together, and the first year affected is the one beginning 1 July 2026. This is the last year in which a practitioner can rely on the old date for such a corporation, and the first in which the file is likely to carry a diary note that has become wrong.

The additions to tax in IRC § 6651 have not changed in structure. The minimum addition for a return more than sixty days late is indexed and therefore moves annually, which makes any figure recalled from memory unreliable within a couple of years.

Exam focus

The date question is the reliable one, and it usually turns on the entity type. A C corporation files in the fourth month; a partnership or S corporation in the third. Where the question gives a June year end for a C corporation, check the year: for a year beginning before 2026 the answer is the third month, and for a year beginning after 2025 it is the fourth.

The penalty computation usually gives tax, a number of months, and asks for the addition. Read whether the failure was to file, to pay, or both. If both, remember IRC § 6651(c)(1) and do not add the two rates together. If neither the return nor the payment was late, there is no addition however unhelpful the corporation has been.

Where a question describes a return filed on time with the tax paid late, the answer is the half-percent rate, and any option computed at five percent is testing whether the candidate read the stem.

Check yourself

1. A C corporation has a taxable year ending 30 June 2027. When is its Form 1120 due, without extension?

Answer: 15 October 2027. That year began 1 July 2026, so it is outside the Pub. L. 114-41 § 2006(a)(3)(B) deferral, which applied only to taxable years beginning before 1 January 2026. The general rule in IRC § 6072(a) applies: the fifteenth day of the fourth month following the close of the fiscal year.

2. The same corporation’s year ends 30 June 2026. When is the return due, and how long an extension is available?

Answer: 15 September 2026, with a seven-month extension to 15 April 2027. That year began 1 July 2025, so it is inside the deferral and inside the Reg. § 1.6081-3(e) exception, both of which turn on the year beginning before 1 January 2026.

3. A calendar-year C corporation files its return on time showing $9,000 of tax and pays three months late. What is the addition to tax?

Answer: $135. There is no failure-to-file addition, because the return was filed on time. IRC § 6651(a)(2) charges 0.5 percent of the tax shown for each month or fraction of a month, so 1.5 percent of $9,000. The five percent rate applies only to a failure to file.

4. A calendar-year C corporation with $60,000 of tax files four months late and pays when it files. What is the total addition?

Answer: $12,000. Failure to file at 5 percent a month for four months is 20 percent, or $12,000. Failure to pay at 0.5 percent a month for four months is 2 percent, or $1,200. Under IRC § 6651(c)(1) the failure-to-file addition is reduced by the failure-to-pay addition for each month both apply, so the total is $12,000 rather than $13,200.

5. A dormant C corporation owing no tax files its return eleven months late. What is the addition?

Answer: nil. Both additions in IRC § 6651(a) are percentages of tax — required to be shown for (a)(1) and shown for (a)(2) — and the corporation has none. The minimum addition for a return more than sixty days late is the lesser of a fixed indexed amount or 100 percent of the tax required to be shown, and that is also nil.