Most conversations about 401(k) audit deadlines revolve around two dates: July 31 and October 15.
Those dates matter for calendar-year plans. But if your 401(k) plan operates on a fiscal year or another non-calendar-year plan year, your Form 5500 deadline falls at a different time of year—and your audit should be scheduled around that deadline.
The basic rule is straightforward: Form 5500 is generally due by the last day of the seventh calendar month after the plan year ends. A plan administrator can generally obtain a one-time extension of up to 2½ months by timely filing Form 5558. If a due date falls on a Saturday, Sunday or federal holiday, the filing may be made on the next business day.
For plan sponsors that require an independent 401(k) audit, that means audit season can happen virtually any month of the year.
Here’s how to determine your deadline—and when you should start preparing.
First, Know Your 401(k) Plan-Year End
Your company’s fiscal year and your 401(k) plan year are not necessarily the same thing. For Form 5500 purposes, the important date is the end of the plan year stated in your retirement plan documents.
A company may operate on a June 30 fiscal year while maintaining a calendar-year 401(k) plan ending December 31. In that case, the July 31 Form 5500 deadline would still generally apply.
So before calculating anything, confirm: What date does our 401(k) plan year actually end? Once you know that date, determining the normal Form 5500 deadline is relatively simple.
401(k) Form 5500 Deadlines by Plan-Year End
The following chart shows the general filing schedule for a 12-month 401(k) plan based on its plan-year end.
| 401(k) Plan Year Ends | Normal Form 5500 Deadline | With Form 5558 Extension* |
|---|---|---|
| January 31 | August 31 | November 15 |
| February 28/29 | September 30 | December 15 |
| March 31 | October 31 | January 15 |
| April 30 | November 30 | February 15 |
| May 31 | December 31 | March 15 |
| June 30 | January 31 | April 15 |
| July 31 | February 28/29 | May 15 |
| August 31 | March 31 | June 15 |
| September 30 | April 30 | July 15 |
| October 31 | May 31 | August 15 |
| November 30 | June 30 | September 15 |
| December 31 | July 31 | October 15 |
*A Form 5558 generally provides a one-time extension of up to 2½ months when properly filed on or before the plan’s normal Form 5500 due date. Actual filing dates can shift when a deadline falls on a weekend or federal holiday.
This means a June 30 plan doesn’t have to organize its audit around the traditional July and October rush. Its normal filing deadline is generally January 31, with an extended deadline generally falling on April 15. Similarly, a September 30 plan generally files by April 30—or July 15 with a timely extension.
