there is a limitaion on itemeized deduction ie that if ur AGI is greater than 166800 ur itemized deduction will be reduced by 3% of the excess amt ... but again there is an exception on that .ie this reduction can reduce ur deduction upto 80 % but not more than that

Suppose let say that ur AGI is 180000 soo it is excess than 166800 (180000-166800)=13200

now 3%of 13200 ie 396 will reduce ur itemised decution

NOw suppose ur itemized decution is say 2000 than it twill be reduced by 396 $ now u will be aloowed the deduction of 2000-396=1604

but this reducing of itemised deduction will be done till ur itemised decution reduces to 80% ie it can be bought down till 400 but not more than that

these are just imaginary numbers to expalin the concept .. i hoep it helps u