Yes it was good to have Schwab take withholding out. Plus the IRS might recalculate the penalty and send you a refund or bill for more, that's common. The amount Turbo Tax figures is just an estimate. Have you filed yet?
You might be able to eliminate the penalty or at least reduce it. You can go to Federal Taxes tab or Personal tab, under Other Tax Situations and select Start by the Underpayment Penalties. You will answer a series of questions that may reduce or eliminate the penalty. Or you can elect to have the IRS figure the penalty for you. It's form 2210.
It's under
Federal or Personal (for Home & Business Desktop)
Other Tax Situations
Additional Tax Payments
Underpayment Penalties - Click the Start or update button
