Lemme see here, the basic pay for an E7 over 18 years of service (no other pay or allowances included like BAQ or Sep-Rats) is $3,803 per month, DFAS 2008 pay scale for base-pay ONLY.
Now the word I got when I hit 20 was I get 1/2 of what my active-duty counter-part gets in base-pay for life, and it's like active duty pay, taxable, so we won't even go there and leave both figures at B 4 tax, 'K?
So my restored retired pay kicked in (YEAH!) and I see DFAS has plonked $1,515 a month into my bank.
I was never great at math BUT 1/2 of an E7 pay @ 20 years (over 18 but not made 21 years) is $1,901.50.