Tax Preparation: What Happens If You Don't File a Personal Income Tax Return by October 15?

Most U.S. taxpayers file their personal income tax by April 15. But many take advantage of the automatic 6-month extension by filing Form 4868, which gives you until October 15 to file.

What happens in you don't file your return by the extended due date? Here are the possible consequences.

Scenario 1: Balance due return.
If you have a balance due, you will pay late payment penalties and interest charges for filing and/or paying your tax return late. Here's how that works.

Late filing penalty. This is also known as the failure-to-file penalty, and it's stiff -- 5% of the tax for each month or part of a month that the return is late, up to 25%.

Example: Let's say you owe $1,000 and you filed the extension on April 15, but October 15 is here and you still don't have the money, so you don't file the return because you think that if you can't pay the tax you're better off not filing the return. Big mistake! If you don't file the return by October 15, you'll pay $50 for each month that the return is late. This penalty applies even if you are late just one day. If you wait five months to file, you'll owe an extra $250.

Better option: if you can't pay the balance due, at least file the return and avoid the 5% per month late filing penalty.

Late payment penalty. Also known as the failure-to-pay penalty, it applies if you have a balance due and do not pay it by April 15. Filing the extension does not eliminate this penalty, because the extension only extends the time to file the return, not the time to pay the tax. The penalty is one-half of one percent of the tax due for each month or part of a month that the payment is late, up to 25%. Obviously, this is much lighter than the late filing penalty.

Interest charges. You will also pay interest on any late payment of taxes, based on the actual number of days that the payment is late and the interest rate currently in effect during the time the payment was not made.

Scenario 2: Refund.
If you are getting a refund, there is no penalty for late filing because the starting point for any penalty calculation is the amount of tax due. No tax due, no penalty. But generally speaking, you are required to file the return within three years of the original due date (including extensions) to get the refund.

If you file your return late and/or pay the tax late, there are other rules that may apply to your situation, so be sure to consult IRS Publication 17 or your local tax professional for more information.