How OPM reads a court order
A court order dividing a FERS annuity has to state the former spouse's share in a way OPM can apply without interpretation: a fixed dollar amount, a flat percentage, or a formula whose inputs are things OPM can determine on its own (5 C.F.R. Part 838). The most common formula by far is the "marital fraction" — half of whatever portion of your career happened during the marriage.
Why the marital fraction usually lands well under 50%
The 50% in the marital-fraction formula only applies to the portion of your service that overlapped with the marriage — not your whole career. Someone who married partway through a federal career, or whose marriage ended years before retirement, ends up apportioning a meaningfully smaller share than a flat 50/50 split of the annuity itself.
Two separate things a court order can cover
A share of the annuity you're currently drawing (what this calculator models) and a former-spouse survivor annuity (a separate benefit that only starts after you die) are both things a divorce decree can address — and often both appear in the same order. This tool covers the first one. For how a survivor election works generally, see the Survivor Benefit Election tool.
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