The specific impact index, or s-index, is introduced as a measure of a scientist's projected impact per paper. The index is complementary to other indices that measure overall impact as it can distinguish between authors maximizing the quantity of their output and authors maximizing the quality of their output. It also can be used to monitor career progress. The main advantage of the new index is that it reduces age bias from older papers that have more time to accumulate citations than do more recent papers. The index was tested on 24 scientists in different fields and of different statures. The overall projected impact estimated from the index correlates well with Hirsch's h-index squared (r2=0.99). The impact of different aging models was evaluated as well.