The cap on Social Security is individual, not collective.

So, if one of you earned more than $128,400 from more than one W-2 then yes TurboTax will adjust and you will see the excess SS withheld on Schedule 5 line 72.

If neither you or your wife individually earned more than $128,400, then you would not be subject to the Social Security Tax Cap. 

Make very sure that you entered your W-2's under your own names so that you do not show excess SS withheld from only one of your names and end up in a mess a couple of years from now when the IRS catches the error.

It looks like the rules might have changed for 2020. I have always prepared returns for my husband and myself first as individuals filing single, then preparing a return with combined incomes and filing as married joint. In the past the taxable social security remained the same after I combined our incomes, but for 2020 our combined taxable social security was pushed up to the max rate although neither of us past the $128K income limit. For us it increased taxable social security by $8k and our tax liability to almost $2K more.

 

I would appreciate any input from someone who is knowledgeable about a change in taxable social security for 2020. Or is there an error on TurboTax?

I've answered my own question after digging a little bit. Due to the CARES act my husband was able to defer most of his RMD's therefore his income fell well below prior years' income. With this his taxable social security rate fell as well. When I combined our returns we were back up to the max 85% taxable rate.

 

This reduced income will help us as well with a lower medicare withholding on our SS checks.

If you file separately  AND  you live together  then 85% of the SS benefits are taxable even if you have no other income and are not normally required to file ... so you must be answering something incorrectly if the SS benefits are not always 85% taxable.   This is the "anti" filing separately rule to keep married couples from trying to circumnavigate the tax laws.  

@Judithz   what do you mean you first fill them out as Single?  It would have to be as Married filing Separate, not Single.  And are you using different account in the Online version or doing separate returns in the Desktop program?  And then using a new 3rd account/return for the Joint return?  Are you doing that just to compare?  

 

To see the Social Security Benefits Calculation Worksheet  in Turbo Tax Online version you would have to save your return with all the worksheets to your computer.   Or if you are using the Desktop CD/Download Software you can switch to Forms Mode (click Forms in the upper right) and click on SS in the list on the left side.