X,
Earlier this month you reported, "I was an E-4 with 4 years of service AD retired in 2012."
Based on that information, your CRSC will be:
1. 4 years AD x 2.5% = 10% longevity multiplier
2. For a current month payment, your average high three for retirement in 2012 will be extrapolated by the COLA increases that occurred since then...to date.
3. The extrapolated high three x 10% will be the longevity portion of retirement pay in real time.
4. Your CRSC will be the amount determined by item 3.
I regret giving you this news, but I hope it is better to learn it now, rather than upon receipt of a payment much lower than what you expected.
Ron