Hi walleye, welcome aboard
Guess you've been around a bit, just waiting to post. I think I can help with your question.
Since this could go a few ways depending on how you did the character generation I'll use the first possibility for the example, career Army then into the Merc trade.
So your PC starts in the Army with a 1st level BAB of +0, a Fort bonus of +0, a Reflex bonus of +2 and a Will bonus of +0. They cycle through to Army level 8 (and character level 8) and end up with a BAB of +6/+1, a Fort bonus of +2, a Reflex bonus of +6 and a Will bonus of +2.
Next the PC joins the Mercenary corp. and in his first level
ADDS a BAB of +1 (total +7/+2), a Fort bonus of +2 (+4 total), a Reflex bonus of +0 (+6 total) and a Will bonus of +1 (+3 total).
As each of those is increased the total is likewise added to.
After level 8 of Mercenary (and character level 16) the PC has totals of BAB of +14/+9/+4, a Fort bonus of +8, a Reflex bonus of +8 and a Will bonus of +6.
At least that's my understanding of it and I'm quite confident in it. I'm sure if I'm in error someone will correct it.
Hope that helped.