So when exactly is this year's income tax deadline?

For years, we've treated April 15 as the official tax deadline — except in years that it isn't.

So put a big red circle around Tuesday, April 17,  as the date you've got to file 2017 income tax returns for both Michigan and the federal government. Taxpayers have until 11:59 p.m. to submit returns by e-file or postmarked through the U.S. Postal Service. 

Taxpayers are looking at another quirky deadline for filing 2017 returns and the change-up is generating confusion. 

What's the reason we get two extra days? 

This year, April 15 falls on a Sunday.

As a result, the Internal Revenue Service typically would shift the filing deadline until the following Monday. 

But Monday, April 16, is Emancipation Day — a legal holiday in the District of Columbia.

So that pushes the filing deadline for all those 1040 returns to Tuesday, April 17. 

"Under the tax law, legal holidays in the District of Columbia affect the filing deadline across the nation," according to an IRS statement. 

The IRS already has received nearly 85.7 million individual income tax returns through March 23, the latest data available. That up 0.5% from the same time a year ago.

About 80% of the returns processed so far have generated tax refunds. The average refund so far this year is $2,925. 

Wondering what's holding up your refund? Check out the Where's My Refund? ‎tool at www.irs.gov and the IRS2Go phone app.

Remember, according to the IRS, tax preparers and tax software will not have additional information on refund dates. Where’s My Refund? remains the best way to check the status of a refund, the IRS said. 

Read more: 

Like zombies, 3 tax breaks return from the dead

Forget to file tax return? Get your refund now

Michigan also has an online tool for checking the status of state income tax refunds. See www.michigan.gov/taxes. 

Michigan's Department of Treasury said more than 4.1 million Michigan taxpayers e-filed returns last year, which is nearly 83% of state income tax filers. 

Limited quantities of printed tax forms have been distributed to public libraries, Michigan Department of Health and Human Services county offices, Treasury field offices and northern Michigan post offices, according to the state. 

Contact Susan Tompor: stompor@freepress.com or 313-222-8876. Follow Susan on Twitter @Tompor.