On the other hand, social security taxes – the biggest tax for more than two-thirds of families – are mildly regressive. Social security taxes as a proportion of income rise gradually from 5% at the 10th percentile to 9% at the 80th percentile, stay there at the 90th percentile, but then fall off sharply to 5% at the top.
另一方面，社会保障税-这是三分之二以上的家庭的最大的纳税部分-是以适度的递减税率来计算的。社会保障税所占的收入中的比例从第10百分位的5 ％ ，逐步增加至80百分位的9 ％ ，一直到90百分位仍停留在此比例上，但到了收入最顶端的阶层又急剧下降至5 ％。这种下降反映了社会保障税有工资上限，（目前为十万二千美元） 。