When is Form 5330 due for a late 401(k) deposit?
The last day of the 7th month after the end of the tax year of the employer. For a calendar-year employer, that is July 31 of the following year. The due date table in the Instructions for Form 5330 (rev. December 2025, read 2026-08-25) states it for section 4975 excise taxes as the "last day of the 7th month after the end of the tax year of the employer or other person who must file this return."
Note the anchor: the employer’s tax year, not the plan year. A plan year ending June 30 changes nothing for a calendar-year employer’s Form 5330 deadline.
An uncorrected failure means a new filing every year
The part sponsors most often miss is not the date, it is the plural. The same instructions treat a late deposit as an ongoing use of money:
“Transactions involving the use of money (loans, etc.) or other property (rent, etc.) are of an ongoing nature and will be treated as a new prohibited transaction on the first day of each succeeding tax year or part of a tax year that is within the taxable period.”
The taxable period ends only at correction (or a deficiency notice or assessment, whichever comes first). So a deposit failure from 2022 that was never fully corrected did not generate one Form 5330. It generates a filing obligation for 2022, another for 2023, another for 2024, each picking up the accumulated transactions, each due the following July 31 for a calendar-year employer. The instructions’ own worked example shows a single loan appearing on two successive years’ filings for exactly this reason. The scale of the population sitting in that loop is measured on the three-year cohort page; whether your own plan is in it is readable by EIN at planremit.com/check.
The extension changed in December 2025: Form 8868, not Form 5558
If the deadline is close, the extension request must go on the right form, and the right form is newer than most checklists:
“Form 5558, Application for Extension of Time To File Certain Employee Plan Returns, is no longer used for an extension of time to file Form 5330.”
The current instructions direct filers to Form 8868 instead, granting "an extension of up to 6 months after the normal due date of Form 5330" provided it is filed on or before the normal due date. And the caution that follows matters more than the extension: "Form 8868 does not extend the time to pay your taxes." The tax is due with the extension request; the extension buys time for paperwork, not for payment. Interest and penalties for late filing and late payment are billed separately.
Two boundaries worth knowing before filing
Correction has a deadline of its own. Filing the return does not stop the exposure; only correction does, and the instructions add that if the transaction "is not corrected within the taxable period, an additional tax equal to 100% of the amount involved will be imposed under section 4975(b)." The 15% arithmetic and what "amount involved" means for late deposits (it is based on the interest, not the deposits) are covered on the cohort page linked above.
403(b) plans do not file Form 5330 for this. The instructions state: "For purposes of section 4975, the term 'plan' does not include a section 403(b) tax-sheltered annuity plan." A late deposit to an ERISA 403(b) plan is still a fiduciary breach with Form 5500 consequences, but there is no section 4975 excise tax on it and no Form 5330 due for it.
Source
Instructions for Form 5330 (rev. December 2025), IRS, read 2026-08-25: the When To File due date table, the Schedule C prohibited transaction instructions, and the extension section. All quotes verbatim.
Published by Neige AI, Inc., last reviewed August 25, 2026. See the method and sources.
This is independent research, not legal or tax advice. It quotes primary sources with citations. Verify anything load-bearing against the primary source itself before acting on it.