Are you ready? Tax day is here.

Tax day, or the last day for U.S. taxpayers to file a 2023 return, falls on April 15 almost every year, unless that day conflicts with a weekend or a holiday. And April 15 is on a Monday this year, so tax day continues as planned for most states.

If you're not ready to submit your taxes today, April 15 is also the last day to file an extension, which grants a six-month extension and greatly reduces any potential penalties or interest rates that can come with filing late.

We know that April 15 is tax day, but why was it chosen, and how long has it been designated as the last day to file taxes? Here's what to know about the history of April 15.

Tax Day 2024 live updates:What to know about extensions, free file, deadlines and refunds

Why is tax day on April 15?

April 15 as the designated last day to file taxes in the U.S. has historic origins.

President Abraham Lincoln first added a federal income tax with the Revenue Act of 1861 to help fund the Civil War. Taxes were based on assessments not voluntary tax returns, the date they were due varied. The act was later repealed, re-adopted and then held unconstitutional.

The 16th Amendment to the Constitution was ratified in 1913, which gave Congress the authority to tax all incomes. The first filing deadline in 1913 was March 1, which was changed to March 15 in 1918 and finally to April 15 in 1955 to allow for more time for people to prepare their returns.

The deadline remains on April 15 today, unless it conflicts with a holiday or a weekend.

Is tax day a federal holiday?

Although it is the last day to submit a federal tax return, April 15 is not a federal holiday. Government agencies, schools, banks, the post office and other businesses will remain open as usual.

Tax day is only delayed if April 15 falls on a weekend or a holiday and if so, the deadline is moved to the next business day, the IRS says.

What other tax deadlines fall on April 15?

Tax Day is not just the deadline to file your federal taxes for the prior year. 

If you earn income that isn't subject to withholding taxes, you're typically required to make estimated tax payments to the IRS. The agency divides the year into four quarterly payment periods, and the first quarterly payment for 2024 is due today.

Most state taxes are also due on April 15. Residents of Massachusetts and Maine have until April 17 to file federal taxes because of state holidays. There are other exceptions. 

Contributing: Daniel de Visé, USA TODAY.