If I paid my est fed tax early each QTR and also overpaid. Why is TT saying I owe an underpayment penalty?

It depends.  You can actually have a refund and still have a penalty for underpayment if there isn't enough paid in for each quarter based on the total tax due.  Here are some of the details that might help you see why you have a penalty.

Generally, you can avoid the penalty if your total timely estimated payments and withholdings are greater than or equal to the lesser of:

• 90% of the total tax after credits for the current year, or
• 100% of the total tax after credits in the prior year
• See one exception below.

You can also avoid the penalty if the amount you owe is less than $1,000 as long as any estimated tax payments you made are timely.

Note: High-income taxpayers. If your adjusted gross income (line 11 of your 2023 Form 1040) is greater than $150,000 (or $75,000 if you're married and file a separate return from your spouse), you can avoid a penalty by paying at least 110% of your total tax from the prior year.

If you have a high amount of income in the last quarter of the year, then it's possible to use an annualized method to reduce it.

• What is Form 2210?
• How do I add Form 2210 in TurboTax?