April 15 is tax day. This means you have to file your tax return by April 15, unless you have permission to file later. You can get permission to file six months later, by October 15, if you file an extension request with the IRS. The extension request must be filed by April 15 to avoid late penalties and interest. You must file form 4868 to get an automatic filing extension until October 15.
If you file your tax return after April 15, you will have to pay a late penalty and interest on the unpaid tax that you owe. The late penalty can be severe, as much as 25 percent of your tax liability. That is $250 on a $1,000 tax bill. In addition, you will accrue interest on all unpaid taxes at the rate of 0.5 percent per month.
Even if you timely file for an automatic six month extension, the extension is only for the filing and not the payment of taxes. You may have a very good reason for extending your filing, but that does not matter. Tax payments are due on April 15, and every day your payment is late accrues interest. You can avoid interest by paying your estimated tax liability, even though you don't have a final calculation.
All late payments bear interest at the rate of 0.5 percent per month of all unpaid taxes. The following example will illustrate. Assume you file an extension request on April 14, and you make an estimated tax payment of $1,000. On October 15, you file your tax return on time, with a tax liability of $1,300. Because you underpaid by $300, you will be charged interest on that $300 for the six-month period between April and October.
Out of Country
The only exception to the April 15 deadline is for taxpayers who are out of the country on April 15. If you are out of the country then you automatically get an additional two months to file your return and pay your taxes. This means you will not begin to accrue interest until June 15. You do not need to request an extension if you are out of the country, the extension is automatic for both payment and filing.