Last Updated: August 30, 2026 Reading Time: 8 min
Your last paycheck arrives, and then the federal retirement system makes you wait. FERS retirement cash reserves are the piece most retirement plans skip: OPM's interim payments cover only 60 to 80 percent of your annuity, the FERS Supplement is excluded from them entirely, and the average claim took 109 days to process as of July 2026. Here is what that gap costs, and the cash number to hit before you file.
The Three Gaps Between Your Last Paycheck and Your Full Annuity
The transition is not one delay. It is three, and they stack.
Gap 1: the interim payment shortfall. OPM starts interim payments after your agency sends it a complete retirement package, and those payments run roughly 60 to 80 percent of your estimated net annuity. The clock starts at OPM receipt, not your retirement date, and agency processing adds its own weeks up front.
Gap 2: the missing supplement. If you retire on an immediate, unreduced annuity before 62, the FERS Supplement bridges you to Social Security. But OPM's retirement Quick Guide is explicit: interim payments do not include the supplement. It arrives only after full adjudication, with back pay. Until then, the supplement portion of your income is zero.
Gap 3: the timing you can't schedule. Your unused annual leave converts to a lump-sum payment under 5 U.S.C. 5551, but the statute sets no payment deadline and OPM warns it may take several months. Meanwhile the TSP stays locked until your agency reports your separation, which can take 30 days.
Everything withheld eventually arrives. The problem is that your mortgage doesn't wait for adjudication.
The Dollar Math: What the Gap Actually Costs Per Month
Two numbers define your monthly gap during processing:
Monthly gap = (25% of your gross monthly annuity) + (100% of your monthly supplement)
Worked example, a GS-12 retiring at MRA with 30 years and a $92,000 High-3:
| Line | Amount |
|---|---|
| Gross FERS annuity (30 yrs × 1.0% × $92,000) | $27,600/yr = $2,300/mo |
| Interim payment at ~75% | $1,725/mo |
| Interim shortfall | $575/mo |
| FERS Supplement (est. 30/40 × $1,700 SS at 62) | $1,275/mo, paid $0 during interim |
| Total monthly income gap during processing | $1,850/mo |
FedTools 2026 analysis. Supplement shown is an illustrative estimate; your actual supplement is roughly your FERS years ÷ 40 × your projected age-62 Social Security benefit.
Your Cash Buffer Target Table
Multiply your monthly gap by a processing scenario. Three months is a fast claim, six months brackets the current 109-day average plus agency lead time, and nine months is the high-backlog case.
| Monthly income gap | 3-month gap | 6-month gap | 9-month gap |
|---|---|---|---|
| $1,500/mo | $4,500 | $9,000 | $13,500 |
| $1,850/mo (GS-12 example) | $5,550 | $11,100 | $16,650 |
| $2,500/mo | $7,500 | $15,000 | $22,500 |
FedTools 2026 analysis. These are planning scenarios, not guarantees; run your own annuity and supplement through the calculators below.
That is the minimum viable buffer: it keeps the lights on while OPM works. It is not the whole answer.
Add the Sequence-of-Returns Cushion on Top
The second reason cash matters has nothing to do with OPM. If a market drop hits in your first years of retirement and an emergency forces TSP withdrawals anyway, you sell more shares at low prices, and the damage to your balance is permanent even when the market recovers. Retirement researchers generally recommend holding one to two years of planned portfolio withdrawals in cash or near-cash for exactly this reason.
So the full target is:
Recommended buffer = minimum viable buffer + about 12 months of your planned TSP withdrawals
If you plan to draw $1,500 a month from TSP, that adds $18,000 to the GS-12 example above, putting the recommended total near $29,000 to $35,000 depending on the processing scenario. A number like that takes 12 to 18 months to build without disrupting TSP contributions, which is why this planning starts well before your retirement date, not the month of.
Where to Hold the Buffer
The buffer's job is availability, not yield. High-yield savings accounts and money market funds fit the processing-gap portion. I-bonds can hold part of the sequence cushion, but remember the 12-month lockup and the three-month interest penalty before five years. Anything that can be down 20 percent the week you need it does not belong in this bucket.
One tax note: the annual leave lump sum is taxed as ordinary wage income in the year it is paid. A December retirement can push it into the next tax year; a January payment stacks it on top of a full year of annuity income. Model both before picking your date, and see our annual leave payout calculator for the gross number.
Calculate Your Own Gap
Use the free FERS Retirement Calculator to get your annuity and supplement estimates, and the High-3 Calculator to confirm the salary base feeding both. Twenty-five percent of the annuity plus the full supplement, times your processing scenario, is your buffer floor.
Frequently Asked Questions
How much of my annuity do OPM interim payments cover?
About 60 to 80 percent of your estimated net annuity, commonly near 75 percent. The withheld portion is paid retroactively once your claim is finalized. Average processing ran 109 days as of July 2026.
Is the FERS Supplement included in interim payments?
No. OPM's Quick Guide states interim payments do not account for the annuity supplement. It starts only after full adjudication, with back pay for missed months.
How fast is the lump-sum annual leave payout?
There is no statutory deadline, and OPM warns it may take several months. Treat it as a bonus when it lands, not a bridge.
How soon can I withdraw from TSP after retiring?
Budget about 45 days: your agency has up to 30 days to report your separation, and the account stays locked until then. After that, requests before noon Eastern generally process the same night.
Does the back pay make the buffer unnecessary?
No. The money arrives eventually, but your bills arrive during the gap. The buffer prevents forced TSP sales in a down market, which is the loss that never comes back.
Related Resources
- OPM Interim Payments Explained: How the interim system works claim by claim.
- Federal Employee Emergency Fund Guide: The working-years companion to this guide, built around shutdown risk.
- State of Federal Retirement Processing 2026: The backlog data behind the 109-day average.
- FERS Retirement Calculator: Your annuity and supplement estimates.
Sources: OPM Retirement Quick Guide · OPM Retirement Processing Status · OPM Lump-Sum Annual Leave Fact Sheet · TSP: Taking Money From Your Account