We got $2000 from IRS for advance child credit. But we did not get letter 6419. So how do we fill box 1? $1000 for each of us, or only $2000 for me for joint filing?

[xmasbaby0]

If you did not receive the letter you still need to enter the total amount that you received during July through December for those advance CTC payments.  Make sure you enter the total of $2000 if that is what you received.   If you enter less than the amount you received it will delay your refund.

You can check your online accounts with the IRS if you are not sure of how much was sent to you.

https://www.irs.gov/payments/your-online-account

The remaining amount of CTC that you can receive will show up on line 28 of your 2021 Form 1040.   Then it will calculate down to the refund you see on line 35a or the tax due on line 37.

PREVIEW 1040

https://ttlc.intuit.com/questions/1901539-how-do-i-preview-my-turbotax-online-return-before-filing

Click on Tax Tools on the left side of the screen. Click on Tools. Click on View Tax Summary. Click on Preview my 1040 on the left side of the screen.

NOTE:   The CTC is indeed a “credit” that can be applied toward any tax liability that you would otherwise have to pay as “tax due”  to the IRS

[DMarkM1]

You can split the advanced child tax credit payments between you and your spouse on your tax return.  However, as long as the total is reported on your joint tax return the tax calculations will be correct even if you put it all in one box.