I worked for a number of years during which I should have been paying into Social Security, but I only paid into CSRS. Can I get any Social Security credit for that work? And, if so, how much will it cost me?
You will get Social Security credit for all that work, and it won't cost you anything. Your agency will send the Social Security Administration a record of your earnings during all the years you should have had Social Security coverage. All of the CSRS contributions you made during those years that are not needed to cover your retirement costs will be transferred to Social Security. This transfer will pay all the Social Security taxes you owe.