I thought that Form 4868 (to get a 6-month extension on my tax return) had the same deadline as tax returns, meaning that it needs to be postmarked by April 15th.
But on page 4 of Form 4868, it says the following:
Private Delivery Services
You can use certain private delivery services designated by the IRS to meet the “timely mailing as timely filing/paying” rule for tax returns and payments. These private delivery services include only the following.
• Federal Express (FedEx): FedEx Priority Overnight, FedEx Standard Overnight, FedEx 2 Day, FedEx International Priority, and FedEx International First.
• United Parcel Service (UPS): UPS Next Day Air, UPS Next Day Air Saver, UPS 2nd Day Air, UPS 2nd Day Air A.M., UPS Worldwide Express Plus, and UPS Worldwide Express.
The private delivery service can tell you how to get written proof of the mailing date.
Why would it recommend a bunch of overnight, next-day, and 2nd-day services if the April 15th deadline is for postmarking? That suggests that the April 15th deadline is actually when it needs to be received by the IRS.
It doesn't even mention the U.S. Postal Service.
So does Form 4868 need to be postmarked by April 15 or received by the IRS by April 15?