The amounts on the estimated tax payment vouchers is considered to be estimated based on the assumption that income and tax withholding will remain the same from year to year. However, the need to make estimated tax payments is based on actual income and tax withholding. Failure to timely pay an amount to satisfy one of the underpayment safe-harbors results in an underpayment penalty. When tax withholding is insufficient, estimated tax payments are needed to make up the difference, although the amount necessary might be different that what TurboTax estimated..
Maryland tax payments follow essentially the same rules as federal tax payments described here:
https://www.irs.gov/payments/underpayment-of-estimated-tax-by-individuals-penalty
