Turbotax does not "calculate" your 2021 estimated tax payments. That calculation is something only you can do because only you know what your 2021 income will be. You are responsible for calculating your own estimated payments and making them on time.
If you underpaid your 2020 taxes, Turbotax may print out estimated tax payment vouchers for 2021. Those vouchers are based only on a snapshot of your 2020 income and other payments, and don't take into account changes in your circumstances that might change in 2021, such as changes in income, dependents, or other credits and deductions. You are not required to use the vouchers at all and they are not part of the accuracy guarantee, since your 2021 taxes can't be calculated from your 2020 income if your situation changes.
