Yes, if you choose CSRS Offset coverage, you can get credit for that deposit service by taking an actuarial reduction. That's because the nature of the service changes from FERS to CSRS time when you elect CSRS Offset coverage. If you remain in FERS, you will have to pay a FERS deposit before you can get credit for the service time. You would not be eligible for the actuarial reduction.
Before you're asked to choose retirement plans, OPM will give you information about your benefits under both CSRS and FERS. They will tell you how much you owe under both. They will also explain how payment of a deposit and the actuarial reduction will affect your benefit.
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