Why whole-year approximations can be off by up to 11 months
A calculator that asks for "years of service today" and a whole-number "retirement age" typically projects your future service as (retirement age − current age) added to what you have now. That math is exact only if you separate on your birthday. Someone planning to retire in, say, March but who won't turn the relevant age until October is actually about 7 months short of what that approximation assumes — or 5 months ahead of it, depending on which direction the rounding falls. For a mid-career or mid-pay-period exit, that gap is worth knowing.
Where to find your Service Computation Date
Your SCD-Leave date appears in Block 31 of your most recent SF-50 (Notification of Personnel Action). It's adjusted for breaks in service, so it's usually a better starting point than your original hire date — but it is set for annual-leave accrual, and it can differ from the service OPM uses for retirement eligibility and your annuity. Prior military service (counted for leave whether or not you've paid the deposit), refunded service you haven't redeposited, temporary or other service that wasn't covered by FERS, and part-time service (prorated for the annuity) may need separate treatment. Your agency HR office can confirm your retirement service computation.
Use the result everywhere else
The decimal-years figure this calculator produces can be used in any other tool on this site (or the full report) wherever it asks for "years of service" — a more precise input than the whole-number estimate most people use. If any of the exceptions above apply to you, adjust it to the service your HR office confirms counts for retirement.
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When Can I Retire From Federal Service? Eligible, Unreduced, and Affordable →
Why 29 years and 11 months is not 30, and every FERS eligibility path in one table.
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