Can I use my account to run a second tax return to estimate taxes for next year?

[bwyld]

can I run a simulation of taxes after filing this years return?

[Critter-3]

NO ... do not mess with your ONLINE account.   But you can use the ESTIMATES section : 

NOTE:  When you open your return back up, do not make any changes in it if it's already been filed.  If you later have to amend the return, it has to start off exactly as it was when it was originally filed.

• Log in and at the Tax Home or in the section "Your Tax Returns & Documents" for 2020, look for a link "Add a State."
• Click on "Add a State."  (you don't really add one.  That's just to open your return back up.)

With your tax return open, search for 1040-es (be sure to include the dash) and select the Jump to link.

1. Answer No to the question Do you want to change your W-4 withholdings for 2020?
2. Answer the questions about things like your 2020 filing status, income, and deductions.

[VolvoGirl]

Or you can set up a new account to test.  You don't have to pay unless you want to print it out.

How to start another return in the Online version

https://ttlc.intuit.com/community/using-turbotax/help/how-do-i-start-another-return-in-turbotax-onli...