December
15 – File Form 5500 if Extension was filed. – 2/28 Plan Year
15 – Return excess contributions for failed ADP/ACP test to avoid penalties –9/30 Plan Year
31 - File Form 5500 with schedules and audited financial statements, if applicable - 5/31 Plan Year
31 – Issue Minimum Distributions to participants who started receiving them in prior year(s) – All Plan Years