Estimating the FERS Supplement

Pinnacle Personnel Services LLC  |  Debbie Hatch 

Question from the Classroom: Clarification of the FERS Annuity Supplement.

“I’m getting conflicting results for my FERS Supplement between what you taught us in class, and what my agency is estimating it to be. Using the worksheet you provided, it’s $871.20. My agency is showing it as $1,615 per month. I have 18 years of FERS civilian service and I have made all of my military deposits. My total creditable service is 31 years.”

Answer: That’s is a big difference! There could be several reasons for the discrepancy. First, the agency calculators are just that – generic calculators. They make some broad assumptions which may or may not be 100% factual for you.

This agency’s calculator states, “all retirement benefit estimates assume you have no outstanding deposits or redeposits. Each assumed high-3 average salary is based on actual salary when available. When not available, we will use an assumed high-3 totaling 97% of your annual basic pay.”

It is Chapter 51 of the OPM CSRS/FERS Handbook that provides source documentation for how to calculate the supplement. It reads:


There is no way to explain all of that in an easy to understand way.


The 4th step on page 27 of the handbook gives us a simplistic way to estimate the supplement.

===> Divide the number of full calendar years of FERS service (only FERS service – no military deposited time, no sick leave, no prior time under CSRS, and only full calendar years 1 January – 31 December) by 40.

===> Multiply the decimal you get from the above step by your estimated age 62 social security amount.

If I estimate the supplement using your 18 years of FERS, it looks like this:

18 divided by 40 = .45 X 1,936 (estimated SS)
= $871.20 / month

If I were to make an assumption (like the generic calculator does) that all of the time creditable for retirement (e.g. military deposited time) is also creditable for the supplement (and to be 100% clear – it is NOT)

The equation would look like this:  31 divided by 40 = .775 X 1,936
= $1,500.40

There’s still a discrepancy – this assumed calculation is $1,500. Your agency is projecting $1,600

This may be because “actual pay” (page 9 of the handbook) is ONLY basic pay. It is not all of the money you may have received, seen on your W2 and therefore typed into the calculator for your estimate.

This is a FERS annuity supplement – it is NOT a “Social Security Supplement.” It then is NOT designed to “mirror your estimated age 62 Social Security”. Rather, the supplement approximates the value of FERS service (ONLY) in a Social Security benefit.

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