For 2021, the IRS extended the income tax due date for millions of Americans. For most people taxes were due back in May. However, if you requested and received an extension, your final deadline to file is today, Fri., Oct. 15.

See: How To Do Your Taxes Last Minute If You Filed an Extension
Find: Everything You Need To Know About Taxes Leading Up to the Extension Deadline

If you fail to meet the deadline, which expires tonight at midnight, what happens thereafter depends on whether or not you owe money to the IRS or your state.

If the IRS owes you a refund, there is typically no fee or penalty for filing late. This is at the federal level though, and whether or not your state enforces a penalty changes from state to state.

If you owe the IRS any money at the end of the year, both penalties and interest will begin to accrue from the day you are deemed late. This will be in addition to a $330 failure to pay penalty enforced under the Taxpayer First Act of 2019.

Most states operate under a system where those who are granted a federal extension also receive an equivalent extension on their state taxes — but it’s your responsibility to check.

The deadline means online filing by tonight midnight or, if you are filing through paper forms, a letter sent that is postmarked with today’s date.

One of the most important changes to consider for the 2020 tax year is the earned income tax credit and the new child tax credit. Ordinarily, these credits are based on earned income, the stimulus relief bill passed this year allows taxpayers to use their 2019 earnings instead of 2020 to determine eligibility. This raises the total amount of refundable credits, specifically for lower-income earners. You are allowed to compare your income from both tax years to see which one works best for you to use to determine your eligibility.

See: The Best and Worst States for Taxes
Find: Billionaires vs. the Middle Class Across America: Who Pays More in Taxes?

The IRS is also offering this year a Free File program through its website here. If you make $72,000 or less, you can use the site make sure you get your taxes filed today before time runs out.

More From GOBankingRates

• 5 Things Most Americans Don’t Know About Social Security

• 8 Ways Homeowners Can Save $1000s Every Year

• Senior Stimulus: How an Additional $1,400 Check Could Help Social Security Recipients Afford Rising Grocery Costs

• Here’s How Much You Need To Earn To Be ‘Rich’ in 23 Major Countries Around the World

This article originally appeared on GOBankingRates.com: Your Taxes Are Due Today if You Filed For an Extension