Looking for an answer to what is the deadline for filing the 2016 US individual tax returns after obtaining the automatic extension, I found multiple references with varying answers. Of course, the ultimate answer is what the IRS considers as last day to file.
Going to the IRS website, I found this page, stating that the last day is October 16, 2017.
However, in the instructions for the Form 1040, it says in page 7 that:
What if You Can't File on Time?
You can get an automatic 6-month extension if, no later than the date your return is due, you file Form 4868.
The 2016 due date was April 18, 2017. According to my understanding of the regular manner in which people communicate time intervals, then a 6-months extension should bring us to an October 18 deadline, rather than October 16.
This is actually a crucial piece of information, because if someone only reads the (official) instructions, he may be late in getting his returns filed. Nowhere in the instructions could I find an explicit mention of the October 16 date.
Why is there a difference between the website and the document?
What happens if I file on the 17th or the 18th?