Originally Posted by AudoBell

A lot of different factors:

-Pay Entry Base Date and Active Duty Base Date are two different things. I.e. you could’ve started Officer Candidate School during college (Pay Entry Base Date Year) but only start active duty after college. So you could have 6 years of active duty but your pay is for an 8 year rank.
-Flight Pay earns you another ~$150-$800/month
-Basic Allowance for Housing can add another ~$800-$4000/month. I’m on the lower end for my location.
-Other random pay (language, special skills, etc)