Extended until July 15th

And if an extension was requested in 2017, then October 15.  

Thanks - this is an original return, not 1040X.

I assume July 15 still appliers?

1040X is not the same as "extended".

When was the 2016 return actually FILED?

See Q22.

https://www.irs.gov/newsroom/filing-and-payment-deadlines-questions-and-answers

---

@BobKamman wrote:

And if an extension was requested in 2017, then October 15.  

---

To add to Bob's comment, if the return was filed before the extended due date, the SOL will run based on the actual filing date rather than Oct 15.

@itonewbie   "if the return was filed before the extended due date, the SOL will run based on the actual filing date rather than Oct 15."

I'm not so sure of that.  IRM just says "Three years after the due date of the return, or three years after the return was actually filed, whichever is later."  That doesn't make sense for returns filed in November, though.  But I always have to look it up.  There's sometimes a question about whether the mailbox rule applies to October 15 returns.  I think it does, but not to refund claims using the "two years since paid" date.  

2016 return has not been filed.

Based on most recent IRS alerts, it appears that any and all filings due by April 15 have been pushed out to July 15.