Help in verifying 1099-B reporting calculation

I sold some stock in 2024 which triggered 1099-B. I am entering that in TurboTax and have some questions as the tax due is significantly larger than I calculated during sale. 

 

First I completed all my taxes before entering 1099-B in TT and I see my taxable income 1040 line 15 is 506,9xx (last two digit omitted for privacy). 

 

The I entered the 1099-B in TT and it calculated the tax which was a good surprise for me. I used some math to calculate the gains on my end 

 

2024 long-term capital gains tax on $84,656.92 when your taxable income is $506,9xx will be

Long-Term Capital Gains Tax (15%)$12,698.54
Net Investment Income Tax (3.8%)$3,217.36
Total Capital Gains Taxes$15,915.90

 

I also had some short term gain,  short-term capital gain on $443.61

Ordinary Income Tax (35%)$155.26
NIIT (3.8%)$16.86
Total Tax on $443.61 Gain$172.12

 

In summary 

 

Type Amount Tax (Incl. NIIT)

Long-Term Gain$84,656.92$15,915.90
Short-Term Gain$443.61$172.12
Total$85,100.53$16,088.02

 

I see TT is generating 413 dollars extra as tax based on these capital gains. Why is there this discrepancy?