Don’t you still have to pay on 04/15?
Evidently, NO — not if you live in Rhode Island (excepting only Bristol County), or certain designated counties of Massachussetts, which got particularly water-logged in the last deluge.
Everybody else better file and pay up on time: Thursday, April 15th. Meaning: Your tax filing must be postmarked April 15th if you are using United States Postal Service to deliver your return (and check, if you owe money).
You should know that IRS nowadays is strongly encouraging taxpayers to "e-file." I can appreciate the efficiency of this option. But it seems to me the "efficiency" works more to the benefit of the "gummint" than it does for taxpayers, the citizens of the United States.
Plus, even if your vendor (e.g., Intuit/Turbotax) tells you federal e-filing is completely "free of charge," it is only so at the federal level. At the e-commerce level, Intuit uses third parties to effect transactions between gummint and taxpayer that, in my case, resulted in something like a $100 transaction fee. So before you think e-filing is "free," read the fine print.