Seeing different long term capital gains tax rate

[newb54]

Before entering my Capital gains:

Total Income: $409,389

Deductions: 26,265

Taxable Income: $371,134

Federal Credits: $2,000

Federal taxes you Owe: $81,740

Refund shown was: $4,343

After entering my Long term capital gains of $52,150

Total Income: $461,539

Deductions: 26,265

Taxable Income: $423,284

Federal Credits: $0

Federal taxes you Owe: $91,877

Tax Due: $7,794

My Long term capital gains are within 15% tax bracket. So I would expect the tax on $52,150 to be $7823.

Why am I seeing going from a refund of $4,343 to Due of $7,794 (a change of $12,137).

ps: I am using Turbo Tax software.

[rjs]

Your long-term capital gain is subject to 3.8% Net Investment Income Tax in addition to the 15% income tax, so the total tax rate on the gain is 18.8%, which would be $9,804. In addition, the increase in income could have side effects. It could reduce or eliminate various deductions or credits. You have to look at your Form 1040 before and after entering the gain to see what else changes. Look at the actual tax form, not the summary screens in TurboTax.

If you have further questions, please tell us what your filing status is.

[rjs]

You are probably also incurring an estimated tax penalty for not having paid enough during the year, through withholding or estimated tax payments, to cover the tax on the capital gain. See if there is a penalty on Form 1040 line 38 that appears or increases when you enter the gain. The penalty gets added to the amount that you owe. That would account for part of the $12,137.