Service Credit
FERS Part-Time Proration Calculator
Part-time federal service counts as full time for every date that decides when you can retire — and then reduces the pension itself by the fraction of the hours you worked. This works out that fraction, and what it costs.
Informational only — not professional advice. This is an independent estimate, not an official one. Only your agency and OPM can compute your proration factor, and they work from your recorded hours rather than the tours you remember. FedAnnuity is not affiliated with OPM or the U.S. government.
Working part time has not delayed your retirement by a day and has not lowered the salary your pension is worked out from. What it does is multiply the finished figure by 95.20% — leaving $30,014 a year instead of $31,528, a difference of $1,514 a year for life.
Age 62 with 5 years of service
| Period | Length | Hours worked | Full-time |
|---|---|---|---|
| Full-timeJul 9, 2001 – Jan 7, 2012 | 10 yr 5 mo 28 d | 21,902 | 21,902 |
| 64 hrs / pay periodJan 7, 2012 – Jan 6, 2018 | 5 yr 11 mo 29 d | 10,013 | 12,516 |
| Full-timeJan 6, 2018 – Jun 30, 2026 | 8 yr 5 mo 24 d | 17,705 | 17,705 |
| Whole career | 24 yr 11 mo 21 d | 49,620 | 52,123 |
| Annuity at full-time rates$31,528 at 1.1% of high-3 × 25.50 years | $31,528 |
|---|---|
| Proration factor§ 8415(g), applied to the finished figure | × 95.20% |
| Your annuity | $30,014 |
The part-time years cost $1,514 a year — $126 a month, for life, before any cost-of-living adjustment is applied to the gap. What they did not cost you is time: all 24 yr 11 mo 21 d of this service counted toward the retirement rule above, and the high-3 was taken at your full-time salary rate.
How this is calculated
Part-time service is treated generously everywhere except one place, and that one place is the last step of the computation. Understanding which is which is most of what there is to know:
- Eligibility: no effect at all. A year worked at half time is a full year of creditable service. It counts toward the 5 years that vest a FERS annuity, the 20 behind an age-60 retirement, the 30 behind an MRA retirement, and the 20 that raise the accrual factor to 1.1% at 62.
- High-3: no effect either. The average is taken from the full-time rate of the position, not from what you were actually paid.
- The annuity: reduced once, at the end, by a fraction equal to the hours you worked over the hours a full-time career would have held.
All three come from one sentence of 5 U.S.C. § 8415(g), which is worth reading once in the original because almost every summary of it drops half:
“… the average pay of the employee, to the extent that it includes pay for service performed in any position on a part-time basis, shall be determined by using the annual rate of basic pay that would be payable for full-time service in the position; and the benefit so computed shall then be multiplied by a fraction equal to the ratio which the employee’s actual service … bears to the total service that would be creditable for the employee if all of the service had been performed on a full-time basis.”
The factor
proration factor = hours actually worked ÷ full-time hours available
annuity = high-3 × accrual factor × years × proration factor
Both sides of the fraction cover all of your creditable FERS service, not only the part-time stretches. A full-time work year is 2,087 hours — the figure fixed by 5 U.S.C. § 5504(b) and the same one the sick leave chart is built on — and a full-time tour is 80 hours a biweekly pay period. That career-wide denominator is what makes the effect of a few part-time years small but permanent: six years at four days a week inside a twenty-five-year career is a factor of about 95%, not 80%.
The order the reductions are applied in does not change the answer. Every reduction in play — the 5%-a-year age reduction under § 8415(h), a survivor election under § 8419, and this factor — is a multiplication, so the tool applies the proration to the finished figure and states it as its own line rather than burying it in the years.
Where the hours come from
OPM builds the fraction from your recorded hours, pay period by pay period, across your whole career. This tool builds it from the tours you enter: a period’s full-time hours are 2,087 per year of its length, and the hours worked are that figure times your tour over 80. The two agree exactly for a tour that did not change, and diverge only within a period whose tour moved — split the period at the change and they agree again. Overtime is not basic pay and earns no credit, so a tour entered above full-time is held at full-time.
Unused sick leave is converted by the same 2,087-hour chart every FERS employee uses, whatever tour you were on, and then rides through the proration with the rest of the annuity. It is not part of the fraction itself — sick leave is credit, not hours worked.
What this does not model
- CSRS and CSRS Offset. The CSRS rule is § 8339(p), and it is a different computation rather than a different number: part-time service performed before 7 April 1986 is credited in full, so OPM splits the career at that date, computes two annuities, and prorates only the later one. Unused sick leave rides in the earlier, un-prorated half. Nothing on this page applies to a CSRS employee with pre-1986 part-time service.
- Intermittent (WAE) service.An intermittent appointment has no regular tour of duty, so it is not prorated — it is credited by the days actually worked, which is a different rule with a different form.
- Leave without pay. Up to six months of LWOP in a calendar year is creditable service; beyond that it is not creditable at all, which shortens the service rather than the factor. Enter creditable service only.
- Military service.Creditable military service enters both sides of the fraction at full-time hours. Enter it as a full-time period if a deposit has been paid for it — and if one has not, see the military buyback calculator first.
- The retiree annuity supplement, which is computed separately and is not included in the figures here.
- Survivor elections.The tool computes an unreduced annuity. A survivor election is a further percentage taken off both the full-time and the prorated figure alike, so it does not change what part-time service costs as a share — only the dollars.
- Rounding. OPM states the factor as a percentage. The arithmetic here carries it unrounded and rounds only for display, so a figure computed by your agency may differ by a dollar or two.
Sources
- 5 U.S.C. § 8415(g) — the FERS part-time rule: the full-time rate for average pay, and the proration fraction applied to the benefit.
- OPM CSRS/FERS Handbook, Chapter 55 — Computation for Part-Time Employees (PDF) — the hours ledger behind the factor, and the CSRS two-part computation this tool does not model.
- 5 U.S.C. § 8339(p) — the CSRS twin of the rule, with its 7 April 1986 boundary.
- 5 U.S.C. § 5504(b) — the 2,087-hour work year the full-time side of the fraction is built on.
- OPM — Part-Time and Job Sharing — the definition of a part-time tour: 16 to 32 hours a week on a prearranged schedule.
Last reviewed: August 2026
Frequently asked questions
Does part-time federal service delay when I can retire?
No. Part-time service is creditable to exactly the same extent as full-time service for eligibility: a year on a half-time tour is a full year toward the 5-year vesting test, the 20 years behind an age-60 retirement, and the 30 years behind an MRA retirement. The proration rule lives in the computation section of the law (5 U.S.C. § 8415(g)) and nowhere in the creditable-service section, which is why it changes the size of the annuity and never its start date.
How is the FERS proration factor calculated?
It is every hour you actually worked across all of your creditable FERS service, divided by the hours the same service would have held at a full-time tour. A full-time work year is 2,087 hours, and a full-time tour is 80 hours a biweekly pay period. The result is career-wide: six part-time years inside a thirty-year career do not reduce those six years, they reduce the finished annuity by a fraction of a percent for every part-time year. OPM computes it from your recorded hours; this tool computes it from the tours you enter, which agree exactly when the tour did not change mid-period.
Is my high-3 based on my part-time salary?
No, and this is the part of the rule that works in your favour. Section 8415(g) says average pay is determined "by using the annual rate of basic pay that would be payable for full-time service in the position" — so a half-time employee earning $56,000 has the high-3 of the $112,000 full-time rate. The reduction for working fewer hours is applied once, as the proration factor, rather than twice by also shrinking the salary the annuity is computed from.
I only worked part-time for a few years — why does that affect my whole pension?
Because the factor is a ratio of hours across the whole career rather than a haircut on the part-time years. The effect is proportional, though, not punitive: three years at half time inside a thirty-year career is 1.5 work years missing out of 30, so the factor is 95% and the annuity is 5% smaller. On a $100,000 high-3 with 30 years at 1% a year, that is $1,500 a year — permanent, and indexed along with the rest of the annuity by every cost-of-living adjustment.
Related tools
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Open tool →High-3 Average Salary CalculatorFind the highest 3 consecutive years of basic pay in your history — the single figure every FERS and CSRS annuity is computed from.
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