A GS-12 in Ohio once told me she had 23 years in. Her official record said 26. She found out 14 months before her target date, and that three-year gap was worth roughly $400 a month for life. She hadn’t lost anything. She’d simply never counted the right pile of paper.
Most federal employees run their numbers on the years they remember working. That’s almost never the number that matters. The figure that drives your annuity comes from your official service computation date, and a dozen small chunks of your career either land inside it or beside it. Get those chunks wrong and every projection downstream bends.
The fastest fix is to stop guessing and let a tool do the counting. When you calculate FERS retirement with a real calculator, the inputs force you to name each period explicitly, which is exactly where people discover the years they forgot. No calculator can guess your history for you, but a good one won’t let you quietly skip it either.
What actually counts as creditable service
Here’s the part that trips people up. Creditable service isn’t one thing. It’s several different buckets, and each one has its own rules about whether it moves your retirement date.
The core bucket is straightforward: any period you were appointed to a position subject to FERS and paid the FERS deduction. Full stop. That’s your baseline, and it’s usually the only number people track.
Then there’s the bucket most people ignore, which is refunded service. If you left federal work years ago and took your retirement contributions back, that time still exists in your record. You can buy it back, and buying it back typically means paying what you withdrew plus interest. I’d almost always recommend running the payback math before dismissing it, because the interest usually looks scarier than the lifetime annuity bump it unlocks.
Military service is its own bucket with its own conditions. Unused sick leave is a third, and it only counts as a boost to your annuity computation, not toward your eligibility date. That distinction matters more than most people realize: sick leave can raise the check without moving the calendar.
The deposit versus redeposit distinction, and why it costs people thousands
If you served on active duty and then moved into civilian federal service, you either made a military deposit into FERS or you didn’t. If you didn’t, that time may or may not be counted depending on when you were hired. This is a hard cutoff issue, not a judgment call, and the Office of Personnel Management publishes the rules governing which service periods apply.
Redeposit is the civilian cousin. It’s what you owe when you previously withdrew your FERS contributions and now want that time restored.
The reason these categories matter is simple arithmetic. Two employees with identical pay and identical hire dates can walk away with annuities that differ by five figures a year, purely because one of them tracked deposits and the other assumed the system would handle it. The system does not handle it. You have to file.
Should you trust a paper estimate or a calculator?
Both, but in a specific order that most people get backwards.
Start with your official personnel records through your agency’s HR portal. That’s the source of truth for dates. Then take those dates into a calculator that breaks out the buckets separately, because a generic retirement calculator will lump everything into one “years of service” field and hide the problem.
Here’s my honest take, and it’s a stance a lot of benefit guides won’t take: the single number at the top of a calculator is the least useful output. What you want is the line-by-line breakdown. If the tool doesn’t show you which periods it credited, you’ve learned nothing you can act on.
While you’re assembling dates, pull your Social Security earnings statement too. According to the Social Security Administration, your recorded earnings history is available to you online, and cross-checking it against your federal service timeline is a fast way to catch a year you’ve mentally written off. I’ve seen it surface two separate periods people had genuinely forgotten.
A workable checklist for the two years before you file
This isn’t glamorous work. It’s calendar work, and it’s the highest-return hour you’ll spend on your retirement.
- Pull your service computation date from your official record. Write it on paper.
- List every gap of 30 days or more in your federal career. Gaps hide creditable service more often than overlaps do.
- Confirm whether you took a refund of contributions at any point. If yes, request the redeposit figure.
- Confirm whether you made a military deposit. If no, get a written estimate of what it costs to make one now.
- Get your unused sick leave balance in writing. It changes the math, not the date.
- Run your numbers through a calculator that shows each bucket separately, then compare the total against your own list. If they disagree, you’ve found something.
The sixth step is the one people skip, and it’s the one that pays. Disagreement is information. When your hand count and the tool’s count diverge, you’ve located either an error in your memory or an opportunity in your record.
What the interest costs actually look like
Redeposit interest accrues over time, and people tend to freeze when they see the total. My read on it is blunt: treat it as a purchase with a lifetime payout, not a penalty. If a $9,000 payback raises your annuity by $120 a month, you’ve bought an income stream at a rate no annuity product on the market will match. Do the division yourself before you decide it’s too expensive.
One more practical note. Federal employment is a big sector with real turnover, and the U.S. Department of Labor tracks the broader workforce trends that shape how often people cycle in and out of public service. Every one of those cycles creates a potential missing-service question for somebody. If you left and came back, you’re exactly the person this article is written for.
The dates you don’t remember are the ones that pay
Your retirement number isn’t hiding. It’s sitting in a personnel file in an accrual line nobody has read since your first year. The work is unglamorous, the payoff is permanent, and the window to fix a deposit or redeposit problem closes earlier than your retirement date does.
So here’s the question worth answering this week: if you wrote down every month you were actually on the federal payroll, including the ones you’d rather forget, how far off do you think your current estimate is?