Turbotax tells me that my property tax of 12000 capped at 10000 reduced my tax due, but I do not see any change in my tax due. Know why?

[SteamTrain]

You may have already hit the maximum 10,000 with State an local income  taxes paid before you entered your property taxes.  (i.e. state taxes withholding)

[ChristieB]

If your itemized deductions do not exceed your standard deduction for your filing status, TurboTax will apply the standard deduction because it brings you the most benefit. This might also explain why you do not see a change in your tax owed/refund when you add your property tax info. 

You can view your deduction amount by taking the following steps: 

1.) On the left-hand side of your screen, click Tax Tools

2.) Click Tools

3.) On the window that pops up, click View Tax Summary

4.) On the left-hand side of your screen, click Preview My 1040

Your deduction amount will be on Line 8 of your Form 1040