How does TurboTax calculate my estimated tax payments?

TurboTax uses the safe-harbor method by basing your estimated tax on either 100% or 110% of the taxes owed on your prior year return. With your information, we determine if you need to make estimated tax payments for next year to avoid an underpayment penalty. Federal and state payment vouchers may print automatically even when you're not expecting them, for example when you're getting a refund. This is correct and based on the safe-harbor calculation.