When it comes to filing your taxes, today is not the day to dawdle.

Tax returns are due today -- April 18, 2017 -- as is any remaining money you owe to Uncle Sam for 2016.

So if you still have an unpaid balance for last year, you'll have to act fast to avoid getting penalized.

The best thing you can do is file your 2016 tax return, or at least file for an automatic six-month extension.

If you don't do either, you'll be hit with a failure-to-file penalty. That will amount to 5% of your unpaid taxes for every month -- or part of a month -- that you don't file for up to five months. So that penalty will cap out at 25% of your unpaid taxes.

On top of that you'll be subject to a failure-to-pay penalty, which amounts to 0.5% of your unpaid taxes every month, for up to 50 months, for a maximum of 25% of your outstanding balance.

Did we mention interest? On top of these penalties, you'll also be charged interest on your unpaid taxes starting on April 19.

Here's what you should do if you owe money but still haven't filed:

At least file something.

As the IRS helpfully notes, "the failure-to-file penalty is 10 times more than the failure-to-pay penalty. So if you can't pay in full, you should file your tax return and pay as much as you can." Or at least file for an extension and include some payment with it.

Learn what your payment options are.

The IRS has a number of payment plans available if you can't pay all that you owe.

If you owe more than $10,000, you might consider hiring a tax attorney, enrolled agent or CPA with experience setting up payment plans to represent you.

"The more that is owed to the IRS, the more complicated it becomes to negotiate with the government," according to Garrett and Deborah Gregory, two former IRS attorneys who wrote the "Guide to IRS Collections for Liabilities under $10,000."

Filing may help you avoid a late-payment penalty

If you've already paid at least 90% of the taxes you owe for 2016, you may be spared the late-payment penalty so long as you at least file for an extension. You will, however, still owe interest on your unpaid balance until it's paid off.

If you're reading this and thinking I don't have to file today because I probably don't owe any more money, file anyway. What if you're wrong and it turns out you do owe money? If you don't file your return or apply for an extension, you'll get hit with the penalties above plus interest.

Second, if you're owed a refund, why wait? The average refund the IRS has paid out so far this year is $2,850.