BRISTOL, Tenn. -

It's the final countdown for those filling their taxes today and if it isn't postmarked by 11:59 tonight, it could mean big fines for you.    

Tax Day is the day many Americans dread, especially if they aren't ready to send in their returns. We spoke to the IRS to find out what you could be fined for and what you're exempt from.

It's the busiest tax day of the year for not only those filing, but also those preparing. "It's been busy since we opened this morning at 6 a.m. It's been busy since we got here," said Joey Smith, tax professional.

We spoke to Mike Georgiades and asked him why he was waiting until the last minute. "I always wait until the last minute, I guess," he said.

Dan Boone, an IRS spokesperson, told us it's ok to wait until April 15, but not a second longer. "The late filing fee can be up to 25 percent of what you owe. That's a pretty steep fee and one you can avoid by filing an extension," said Boone.

Boone says a late payment can also cost you some cold hard cash: about half a percent per month that it is not paid, on top of an up to 5 percent interest rate.

Those fees are why Carolyn Lass files early. "Whether I'm getting money back or not, I like to get rid of it," said Lass.

But others, like Georgiades, need more time. "I'm not sure I'm doing it right, I misplaced a few papers. So I'm trying to get an extension to make sure," said Georgiades.

Tax professional Joey Smith warns everyone filing for an extension to be sure to send in money too. "It's not an extension to pay, just an extension to file," said Smith.

Smith says you should send in an estimate of what you think you will owe. "Sending something is better than nothing. If you overpay they're going to send it back to you," he said.

"[Send] as much as you can with the extension. If you owe, that will help reduce the late payment penalty and any interest you might owe," said Boone.

Boone told us there are exceptions when filling late. "You can always ask for a battement of penalties if it was something that was unavoidable and unpreventable," said Boone.

Smith tells News 5 that for everyone else, make sure you turn it in and on time."They don't want those penalties and interest put on them, come back, and get them later on. Make sure you get your return done today,” said Smith.

If you're running behind on filing your taxes, we checked with the local post offices in the area and found out many are only opened until 5 p.m. However, the post office on State of Franklin in Johnson City will be opened until 7 p.m. tonight.