After you file

KittyM · ‎June 1, 2019

Unfortunately, you cannot file a Form 3115 after the due date of the return for the year you are filing it, including extensions. From the IRS' publication Instructions for Form 3115

"Except if instructed differently, you must file Form 3115 under the automatic change procedures in duplicate as follows.

Attach the original Form 3115 to the filer's timely filed (including extensions) federal income tax return for the year of change. The original Form 3115 attachment does not need to be signed.

File a copy of the signed Form 3115 to the address provided in the address chart on this page, no earlier than the first day of the year of change and no later than the date the original is filed with the federal income tax return for the year of change."