How to Update Your Address and Contact Information With Medicare

What "COB" means and why you need to update it

COB stands for Coordination of Benefits — it tells Medicare which insurance you have besides Medicare, and in what order to pay claims. If you have a second insurance (from a current or former employer, a spouse's plan, Medicaid, or TRICARE), Medicare needs to know about it so the right plan pays first and the other pays second. When you move, change jobs, or lose coverage, your COB information becomes outdated, and claims may be delayed or denied.

Updating your COB is different from changing your address alone. Your address update tells Medicare where to send mail. Your COB update tells Medicare what other insurance to coordinate with. You may need to do both, and they happen through different processes.

Key Takeaways

COB (Coordination of Benefits) tells Medicare what other insurance you have and which plan should pay first on your medical claims.
You can update COB information by calling Medicare at 1-800-MEDICARE, through your online Medicare account, or by mailing a signed form to your local Social Security office.
Changes to employer coverage, retirement, or loss of other insurance require a COB update within 30 days to avoid claim delays.
Medicare may contact your other insurance company to verify your coverage, so make sure the information you report is current and accurate.
If you have Medicaid or TRICARE in addition to Medicare, those programs also need to know about your Medicare coverage for proper coordination.

Update COB by phone with Medicare

The fastest way to update your COB is to call 1-800-MEDICARE (1-800-633-4227). Have your Medicare card, any other insurance cards, and a list of coverage dates ready. The representative will ask you what other insurance you have, when it started, and whether it is still active. They will enter the information into your Medicare record while you are on the call.

Medicare's phone lines are open Monday through Friday, 8 a.m. to 8 p.m. Eastern time. Wait times are often shorter early in the morning or late in the afternoon. If you use a relay service or TTY device, call 1-877-486-2048.

Update COB through your online Medicare account

If you have set up a Medicare.gov account, you can update some COB information yourself without calling. Go to Medicare.gov, sign in with your username and password, and look for "Personal Health Information" or "Coverage" in your account menu. Not all COB changes can be made online — complex situations or changes to employer coverage may still require a phone call.

Creating a Medicare.gov account takes about 10 minutes and requires your Social Security number, email address, and Medicare number. Once you are logged in, you can also see your claims history, read your Medicare card, and check your coverage details anytime.

Update COB by mail

If you prefer to update COB in writing, you can mail a signed letter to your local Social Security office. The letter should include your Medicare number, the name and type of your other insurance, the policy or group number, and the dates the coverage started and ended (if applicable). Mail it to the Social Security office that serves your area — you can find the address at ssa.gov or by calling 1-800-772-1213.

Mailed updates typically take two to four weeks to process. Keep a copy for your records and consider sending it certified mail so you have proof of delivery.

When you must update COB right away

Report changes to Medicare within 30 days of when they happen. The most common situations are: you retire and lose employer coverage, you start a new job with health insurance, your spouse's coverage ends, you turn 65 and become may be able to access for Medicare, or you lose Medicaid. Each of these changes affects which insurance pays first on your claims.

If you do not report a change quickly, Medicare may pay claims as the primary payer when your other insurance should have paid first. This can leave you with unexpected bills, and correcting it later is time-consuming. Your doctor's office or pharmacy may also flag the problem when they try to bill, but it is better to update Medicare proactively.

What information Medicare will ask for

Be ready to provide the name of your other insurance company, the type of plan (employer group health plan, retiree coverage, Medicaid, TRICARE, Veterans benefits, or other), your policy or member ID number, your group number if you have one, and the dates your coverage started and ended. If the coverage is through a spouse or family member, have their name and Social Security number available.

If you are not sure of all these details, check your insurance card or the most recent explanation of benefits (EOB) from that plan. If you have lost the card, call the insurance company directly and ask them to confirm your policy number and group number.

What happens after you update COB

Medicare will verify your other coverage by contacting that insurance company. This usually takes one to two weeks. Once verified, your COB record is updated and future claims will be processed with the correct coordination. Past claims that were processed incorrectly may be reprocessed, though this can take several weeks.

You will not receive a confirmation letter for every COB update, but you can check your Medicare account online or call 1-800-MEDICARE to confirm the change was recorded. If you do not see the update reflected after two weeks, call again to follow up.

Frequently Asked Questions

Do I need to update my address separately from my COB?

Yes. Updating your address tells Medicare where to send mail. Updating COB tells Medicare what other insurance you have. You can do both in one call to 1-800-MEDICARE, but they are separate pieces of information in your record.

What if I have both Medicaid and Medicare?

Tell Medicare you have Medicaid and provide your Medicaid number. You should also report your Medicare information to your state Medicaid program so they know to coordinate benefits. Contact your state Medicaid office for instructions on how to report Medicare coverage.

Can I update COB if I am on a Medicare Advantage plan?

Yes. Call your Medicare Advantage plan directly first, as they manage your benefits. They will update their records and may also notify Medicare. You can also call 1-800-MEDICARE to update COB in your main Medicare record, which helps with coordination across all your coverage.

What if my employer coverage ends but I do not know the exact date?

Provide the month and year, or the date your final paycheck was issued. Medicare will work with the information you have. If you need the exact date, call your employer's benefits department or check your final pay stub — it usually shows your coverage end date.

Will updating my COB change my Medicare premiums?

No. Updating COB does not change what you pay for Medicare Part B or Part D. It only tells Medicare how to coordinate with your other insurance when paying claims. Your premiums are based on your income and enrollment status, not on COB information.

This guide is for general information only and is not medical, financial, legal, or other professional advice. For decisions specific to your situation, consult a qualified professional. See our Editorial Policy.