The decision to stay on your employer group plan or switch onto Medicare often comes down to the Health Savings Account, also known as an HSA.

If you move to Medicare at 65:
The IRS requires that both you and your employer discontinue contributions to your HSA once you enroll in Medicare Parts A and/or B.

Depending on your arrangement with your employer, you could be receiving a substantial amount toward your HSA each year from your employer, and may affect whether you decide to switch to Medicare.

If you move to Medicare after 65:
If you enroll in Medicare after your 65th birthday month, Medicare will look back to your 65th birthday month OR six months (whichever is closest) to see if contributions were discontinued.

How HSA funds be used once you are on Medicare:
HSA Funds previously accumulated may be used for future qualified expenses. You can use your HSA dollars for things like Part B premiums, Medicare Advantage premiums, copays, and coinsurance, and Part D premiums and expenses. 

HSA funds may not be used to pay for Medicare Supplement premiums, so just keep that in mind as you look to see how you can make the most of your HSA dollars.