But $9 an hour is still a far cry from what workers really deserve, a 2012 study finds.

The minimum wage should have reached $21.72 an hour in 2012 if it kept up with increases in worker productivity, according to a March study by the Center for Economic and Policy Research. While advancements in technology have increased the amount of goods and services that can be produced in a set amount of time, wages have remained relatively flat, the study points out.

Even if the minimum wage kept up with inflation since it peaked in real value in the late 1960s, low-wage workers should be earning a minimum of $10.52 an hour, according to the study.