Can I file two years of tax returns at the same time?

NO!!!!!!!!

Each tax year has to be filed separately using the forms for the specific tax year.  They cannot be combined in any way--do not even put them in the same envelope when you mail them.  Software for past years is available back to 2017.  Any earlier years can only be prepared on paper forms by hand--and those refunds have been forfeited now.

The current online program can only be used for a 2020 return--no other year.  And if you did not file a 2019 return you will have trouble e-filing 2020.  When it asks for your 2019 AGI try using zero.  If zero does not work then you have to print, sign and mail 2020.

Online preparation and e-filing for 2017, 2018 and 2019 is permanently closed.

To file a return for a prior tax year

 If you need to prepare a return for 2017, 2018, or 2019 you can purchase and download desktop software to do it, then print, sign,  and mail the return(s)

https://turbotax.intuit.com/personal-taxes/past-years-products/

You may also want to explore purchasing the software from various retailers such as Amazon, Costco, Best Buy, Walmart, Sam’s, etc.

Remember to prepare your state return as well—if you live in a state that has a state income tax.

https://ttlc.intuit.com/community/state-taxes/help/how-do-i-contact-my-state-department-of-revenue/00/25573 

When you mail a tax return, you need to attach any documents showing tax withheld, such as your W-2’s or any 1099’s.  Use a mailing service that will track it, such as UPS or certified mail so you will know the IRS/state received the return.

Federal and state returns must be in separate envelopes and they are mailed to different addresses.  Read the mailing instructions that print with your tax return carefully so you mail them to the right addresses.

Note:  The desktop software you need to prepare the prior year return must be installed/downloaded to a full PC or Mac.  It cannot be used on a mobile device.

If you are getting a refund, there is not a penalty for filing past the deadline.  If you owe taxes, the interest/penalties will be calculated by the IRS based on how much you owe and when they receive your return and payment. The IRS will bill you for this; it will not be calculated by TurboTax.

Refunds for tax years 2016 or earlier have been forfeited and will not be paid to you even if shown on the tax return form.  But if you owe tax due, you will still have to pay, and you will be billed later for the interest and penalties owed.

Since you are filing a late 2019 return, the IRS will not have a 2019 AGI in the system for you.  When the 2020 software asks for your 2019 AGI so that you can e-file 2020, use “zero.”  If you cannot e-file by using zero then you will have to print, sign and mail your 2020 return.

You’ll likely get a letter from IRS regarding 2020 income on 2021 return. All you can do now is wait to see if IRS rejects its once they open on 1/24. It will likely be delayed for review to figure out where the 2020 income  came from. You will need to file a 2020 return and amend your 2021 return to remove 2020 income. 

@Josegon11 Please explain what you did to file a 2020 return.   The current online software is only for 2021 returns.   The only way to correctly file a 2020 return is to use 2020 software and print, sign and mail the 2020 return.  Is that what you did?

Yes. You can file two years of tax returns, however, they must be completed separately. For example, you would have to input your 2020 tax forms in your 2020 tax return and your 2021 tax forms in your 2021 tax return. 

In addition, to prepare a new prior-year return, you'll need to purchase and download that year's TurboTax software for PC or Mac, as TurboTax Online and the mobile app are only available for the current tax year.

@MsnDld2038