If you have any part-time service in your work history, the more part-time service you have in your career, the greater the reduction will be versus having spent those years as a full-time employee. Here’s how your annuity will be calculated:
1. Your actual time worked will be compared with the number of full-time hours you could have worked. That includes any time you worked in excess of your official schedule tour-of-duty, as long as it doesn’t exceed the amount of hours you could have worked part-time.
2. Divide the actual hours worked by the total full-time hours available. This will give you the proration factor, rounded to the nearest percent.
3. Now compute the amount of annuity you would have received if you worked full time, using either the CSRS or FERS formula that applies to your period of part-time service.
4. Finally, multiply the result by the proration factor. This will tell you how much annuity you are entitled to.
Note: A former policy created a complex formula for CSRS employees that in effect lowered the value of part-time work for them and discouraged them from working such a schedule later in their careers. That has not been in effect for retirements since 2009, although many employees apparently still believe it is in effect.