What’s the best month to retire from the military?

There's only one COLA a year — not quarterly ones.

Military retired pay gets a cost-of-living adjustment once a year, effective December 1 (it lands in your January check). The percentage is the same for every retiree that year — it tracks inflation (CPI-W) from one year's summer to the next.

Your retirement month sets the size of your first COLA.

Your very first December COLA is prorated by how long you'd already been retired, measured in quarters:

• Jan–Mar: you've been retired most of the year → nearly the full COLA.
• Apr–Jun: a bit less.
• Jul–Sep: less still.
• Oct–Dec: you just retired → 0% that first December.

That first-year gap is locked in for life.

After year one, everyone gets the same full COLA every December. So a difference created by your retirement month doesn't wash out — it compounds for 25+ years. That's also the "trap": the first-COLA slice steps down by quarter while serving longer raises your base pension smoothly, so crossing a quarter line (say June → July) can leave you drawing less for life despite serving an extra month.

So which month is "best"?

It depends on inflation. In a calm year the extra pay from serving longer usually outweighs the COLA timing, so a later month wins. In a high-inflation year (try the 2022 stress test) the first COLA is huge and retiring early can win big. The "COLA boost" column isolates the COLA alone; "Annual (year 1)" is the real, combined number.