How can I examine the details for "estimated tax penalties" that turbo tax computes?

To calculate and post a penalty.

1. Start at Other Tax Situations on the side banner.
2. Scroll to Additional Tax Payments
3. Select Underpayment Penalties
4. You chose to let the IRS bill you later.
   1. Choose continue to have the IRS do the calculation.
   2. Select Let’s Figure It Out to calculate the penalty amount.
5. Continue through the interview.

The underpayment penalty may apply if :

• The amount of tax you paid during the tax year is less than 90% of the tax that you owed for the current year. 
• The amount you paid during the tax year did not equal 100%, (110% for higher incomes) of your taxes owed the prior year. 
• The IRS also says you can probably avoid the penalty if the amount you owe is less than $1,000, after subtracting withholding and refundable credits.

To avoid this situation it is recommended that you adjust your W-4 with your employer, or pay estimated taxes.