If you are referring to 2019 estimated tax payments then see this TurboTax support FAQ - https://ttlc.intuit.com/community/tax-payments/help/can-turbotax-calculate-next-year-s-federal-estim...
If you are referring to your tax liability or a tax refund for 2019 then use the TurboTax calculator TaxCaster - https://turbotax.intuit.com/tax-tools/calculators/taxcaster/
What-if worksheets are available but only if using the TurboTax desktop CD/Download editions.
