TurboTax uses a couple of ways to calculate your estimated tax payments. Though the vouchers are helpful, they are not exact.
Likely your vouchers indicated 90% of your prior-years taxes due, and you had a higher income than anticipated. Or perhaps you are a higher-income individual, in which case you'd be required to pay 110% of your prior year's taxes in estimated tax payments. I'm sharing a link to a TurboTax FAQ that will explain how much the IRS expects from you on a quarterly basis.
How does TurboTax calculate my estimated tax payments?
*** I am NOT a tax expert. I am a seasoned TurboTax user, and volunteer to provide assistance to TT users. Nothing I post is to be considered TAX ADVICE; I bear no legal liability for responses.***
