Taxes postmarked by April 15th or due *on* April 15th?

Factual Questions
1

I usually pay before the deadline, but not this year. So do I need to mail it today, or am I OK as long as it’s postmarked by the 15th?

(Yes, I could probably find this online, but I need to catch the 1pm mail if it’s today and I know how lightning fast my fellow dopers are. :))

2

You need the *postmark * on April 15 or earlier. In practice, you could probably miss it by a day or two without hassle, but it’s best not to push it.

3

Thanks ElvisL1ves!

4

Postmarked 4/15. You’ll notice that all post offices are open till a little after midnight on that date each year.

5

Cecil answerd this one as well:

http://www.straightdope.com/classics/a960405.html