What us the underpayment penalty

[KarenJ2]

The underpayment penalty is assessed if you did not pay enough tax throughout the year, either through withholding or by estimated tax payments.

• You avoid this penalty if you either owe less than $1,000 in tax or 
• If you paid 90% of your 2019 tax or 100% of your 2018 tax.

For more information, refer to Publication 505, Tax Withholding and Estimated Tax.  or the instructions to Form 2210 for waivers allowed.2019 Instructions for Form 2210

[roygo]

You reply correctly stated that there is no penalty for underpayment if one pays at least 90% of what one owes by Jan 15.  Why, then, does Turbo Tax calculate a penalty when I clearly made the 90% threshold.

  roygo

[KarenM90]

Did you pay your tax through estimated payments?  Were they paid on time?  

If you don't pay enough tax through withholding and estimated tax payments, you may be charged a penalty.

You also may be charged a penalty if your estimated tax payments are late, even if you are due a refund when you file your tax return.