KEY TAKEAWAYS Which system you're under is determined by your DIEMS date — Date of Initial Entry into Military Service. If you joined on or after January 1, 2018, you're in BRS. If you joined before that and didn't opt in during the 2018 window, you're in High-3. This is not a choice you can revisit. The core trade-off: High-3 pays a larger pension (2.5% per year = 50% at 20 … [Read more...] about BRS vs. High-3 Military Retirement 2026: Which System Are You Under and What Does It Pay?