In TurboTax Online, you can start as many returns as you like for free to see the impact of changing state returns. This would require you to re-input your Federal information into a new pseudo TurboTax account under a different user name but you could change your Personal Info to a fake address for the state you would like to compare. You could monitor your amount of state tax due at the top of the page or go to right hand column and click:
- Tax Tools
- Tools
- View Tax Summary
- Preview your State return
There you could see the amount of state tax for the state you requested in the My Info section. You can then compare that state tax number to your actual state tax number from your true TurboTax account.
