15 - File Form 5500 if Extension was filed. - 3/31 Plan Year

15 - Return excess contributions for failed ADP/ACP test to avoid penalties - 10/31 Plan Year

31 - Distribute Form 1099-R for distributions processed in previous calendar Year - All Plan Years

31 - File Form 945 which reports Form 10999-R income tax withholdings. (may have until February 10 if certain conditions are met.) - All Plan Years

31 - File Form 5500 with schedules and audited financial statements, if applicable - 6/30 Plan Year