Here are the steps you, your agency and OPM need to accomplish as you move from being an employee to a retiree:
What you need to do
Attend a pre-retirement seminar. If one is offered by your agency that’s great. If it isn’t see if they will give you time off to attend one held elsewhere, and even pay for it.
Next, review your Official Personnel Folder (OPF) to be sure you were getting credit for all your civilian and military service, determine the date on which you’d be eligible to retire, make sure that that you’d be able to carry your health and life insurance into retirement, check your Designation of Beneficiary forms to be sure they were up to date, and get estimates of your retirement annuity (and Social Security benefits, if applicable)
What your agency needs to do
Most importantly, your agency needs to confirm that you are eligible to retire as of your chosen date. Then they have to prepare a Certified Summary of Federal Service, which you’ll need to review to be sure all your service has been accounted for. After that, they need to verify that you are eligible to continue coverage under the Federal Employee’s Health Benefits (FEHB) and Federal Employees’ Group Life Insurance (FEGLI) programs, prepare the papers necessary to separate you from the service, authorize your final salary check and lump sum payment for unused annual leave, close out your Individual Retirement record, and forward your retirement package to OPM’s Retirement Operations Center on a Register of Separation and Transfers.
What OPM needs to do
Once the package reaches OPM’s Retirement Operation Center, it will send you a letter acknowledging receipt and provide you with a claim number. Don’t toss this away. You’ll need to use that number every time you check with OPM.
If everything is in order, they’ll authorize interim annuity payments. Those payments will show any deductions that have been taken out, such as taxes and FEHB premiums. In the meantime, they’ll complete the processing of your retirement application and determine the amount of your monthly annuity. How long the process takes will vary depending on such things as whether additional information is needed, and the workload OPM’s staff is facing.
Interim payments are a percentage of a rough estimate of your final annuity—often around 80 percent but potentially much less. OPM does that to avoid overpaying you.
Any shortfall will be made up once you start receiving your full annuity payments, but you might not start receiving that for several months if not longer. Make sure that you have a backup source of funds to carry you for the meantime.
See also, how to calculate an annuity under FERS and CSRS at ask.FEDweek.com