Methodology
How FERS Planner Calculates Your Annuity — Methodology
A plain-English walkthrough of how FERS Planner uses your inputs, documented FERS rules, disclosures, and source review.
Short answer
You enter dates, service history, and a high-three salary estimate. FERS Planner applies documented FERS rules for supported V1 cases and explains the result with sources, warnings, and scope limits.
FERS Planner is independent and not affiliated with OPM. Results are educational estimates, not official benefit decisions.
Last reviewed 2026-04-25
In plain English
In plain English: you enter your dates, service history, and high-three salary estimate. FERS Planner applies documented FERS rules to produce an educational estimate and explain which retirement path your scenario appears to match.
What the calculator does
The calculator collects dates, salary estimates, and a selected V1 retirement scenario. Those inputs are validated before the documented rules are applied.
The rules-based calculator checks whether the scenario is inside the current product scope and returns a clear result for the result page.
What the calculator intentionally excludes
The current V1 estimate covers regular immediate, MRA+10 immediate, MRA+10 postponed, and deferred retirement paths for non-USPS FERS employees. It does not make official benefit determinations.
Unsupported cases are not estimated. USPS/PSHB, disability retirement, special provision retirement, and transferred-to-FERS with a CSRS component remain outside V1.
How we handle changes
Each result includes a last-updated date, methodology link, source link, and disclaimer language. When a rule changes, the calculator behavior and support pages should be reviewed together.
Source-backed content is written in plain English first, then covered by tests before it becomes calculation behavior.
Accuracy statement
We compute FERS estimates from published OPM formula guidance and source links, then keep the calculator scope narrow so unsupported cases are flagged rather than guessed.
We do not publish an accuracy percentage or official-estimate match claim until a documented validation set exists. Treat each result as an educational planning estimate, not a substitute for your agency or OPM calculation.
We do not replace your official OPM retirement estimate — we help you decide which date to request one for.
How the estimate is organized
| Step | What happens | What not to assume |
|---|---|---|
| Inputs | You enter dates, service start, retirement date, and high-three salary estimate. | The site does not ask for SSN, employee ID, or agency login credentials. |
| Scope check | The calculator checks whether the scenario is inside the supported V1 retirement paths. | Unsupported retirement cases are not estimated. |
| Result | The result page shows estimate, eligibility, warnings, methodology, sources, and last updated language. | The result is not an official OPM determination. |