SEPIRA Due Date

[Randall]

Contributions are allowed up to the extension due date.  Just to double check, this means the Oct 15 due date even if the actual return is filed before that date, say Sept 1?  Just double checking. 

[Lion EA]

This is from the FAQs at IRS.com, so you'll want to dig deeper to an authoritative source: 

https://www.irs.gov/retirement-plans/retirement-plans-faqs-regarding-seps#contributions

When must I deposit the contributions into the SEP-IRAs?

You must deposit contributions for a year by the due date (including extensions) for filing your federal income tax return for the year. If you obtain an extension for filing your tax return, you have until the end of that extension period to deposit the contribution, regardless of when you actually file the return.