The 2021 tax deadline was pushed back to May 17 this year, instead of the usual April 15 Tax Day. With under two weeks left to file, many Americans are considering filing for a tax extension instead. This year, filing your tax return   might be more important than ever because of the way stimulus check payments and adjusted gross income are intertwined. For example, on top of a larger tax refund you could also be in for a "plus-up payment" for your third stimulus check. And your 2021 tax information will also be critical in determining the amount you're owed for the newly revised child tax credit. (Use CNET's child tax calculator to see how much you'll get.)

The earlier you file, the earlier you'll receive any and all money coming to you, and the less likely you'll have to jump through additional hoops like filing a tax extension, retroactively claiming child tax credit money or filing a payment trace to claim missing stimulus check money.

Here's what you need to know about this year's Tax Day and how moving it back could affect you. And here's how your tax return this year could bring your more money and how your state may already owe you hundreds of dollars (it takes two minutes to find out). This story was recently updated with new information.

What your 2020 taxes have to do with stimulus plus-up payments

The IRS is looking at your 2020 federal taxes to determine if it underestimated the amount of money you received with the third stimulus check. If the IRS based your payment on your 2019 tax return but your 2020 federal tax return shows you qualify for more money for the third stimulus check, the IRS will send you the difference as a separate plus-up payment.

How the May 17 tax deadline affects stimulus checks

The IRS uses information on your 2020 tax return, if it has it, when it determines the amount you'd get in your third stimulus check. Specifically, the IRS looks at the AGI, or adjusted gross income, on your 2020 form to help figure out your payment, using a new stimulus check formula. 

But the tax agency will use your 2019 return if your 2020 taxes haven't been accepted by the time your payment is sent. That could work in your favor if your income from 2019 was lower than your income from 2020 (you won't have to return the money in most cases). 

However, if your 2020 tax return would bring you a larger third stimulus check, like if you have more dependents, you'd want to file as soon as possible, so the IRS processes your 2020 taxes before releasing your third stimulus check. Here's what people who don't normally file taxes should know.

2020 taxes and the 2021 child tax credit

The child tax credit is different this year. You're eligible for more money per qualified child, and eligible parents will start receiving checks as soon as July on a monthly basis through the end of 2021. A second sum will arrive with next year's tax refund. Your 2021 AGI is crucial for determining how much money you'll actually get, and unlike stimulus checks, you will need to return any overpayment.

What the May 17 deadline means for your missing stimulus money

Your federal tax returns this year are also how you'll recover any money the IRS owes you from the first two stimulus checks. If you either didn't get a payment or got less than you were eligible to receive, you can claim that money on your federal tax forms as a rebate credit when you file this year. That goes for nonfilers, too -- those who aren't normally required to file a tax return. If you wait to file your taxes closer to a new, later due date, you're also waiting to receive your money, which will be bundled into your tax return.

Is your state's tax deadline the same as the federal deadline?

This year, according to the Association of International Certified Professional Accountants, 36 states have shifted back their deadline. Check with your state's tax agency for the specific deadline.

What if you can't make the May 17 tax return due date?

If you need time beyond May 17, you can file a tax extension, which gives you more time to complete and send your paperwork to the IRS. The IRS said individual taxpayers don't need to file forms or call the IRS to qualify for the extension.

The new extension doesn't get you off the hook for estimated tax payments, however. The IRS said the May 17 deadline doesn't apply to those who make estimated payments, which were still due on April 15.

For more details on taxes this year, we spell out the difference between a tax refund and a tax return and how tax season is different in 2021.