The numbers that decide who pays first
Here's what to do, in 4 steps.
Here's the order I'd work through if I had Medicare plus another insurance and didn't know which was paying first.
-
Identify every coverage you have
Make a one-page list: Medicare Part A/B effective dates, any employer or retiree plan (and the employer's size), workers' comp claims still open, auto/no-fault policies, VA enrollment, TRICARE status, and any pending liability case. This list is the input to every MSP decision — you cannot get the order right without it.
Time: 30 minutes Cost: Free 42 CFR § 411.20 (MSP scope)
-
Return your MSP questionnaire
If CMS or your Medicare Administrative Contractor sends you a Medicare Secondary Payer questionnaire (also called the Initial Enrollment Questionnaire or COB Initial Enrollment Form), fill it out and send it back. Failing to respond is a top-tier reason claims get denied or delayed — the system literally cannot tell who pays first without it.
Time: 15 minutes Cost: Free CMS COB&R Center: 1-855-798-2627
-
Tell Medicare when coverage changes
When you start or stop a job with employer coverage, get into a car accident, file a workers' comp claim, or settle a liability case — call the Medicare Coordination of Benefits and Recovery Center at 1-855-798-2627. Reporting changes prevents Medicare from paying primary by mistake and then trying to recover from you later.
Time: 20 minutes Cost: Free CMS COB&R Center
-
Get help if a settlement is involved
If you have a workers' comp, no-fault, or liability settlement on the table — or you've been told you owe Medicare a conditional-payment refund — talk to a SHIP counselor at 1-877-839-2675 or call the COB&R Center. Workers' Comp Medicare Set-Asides have their own rules, and getting the allocation wrong can cost you Medicare coverage on related care for years.
Time: 1 hour Cost: Free SHIP National (1-877-839-2675)
Dr. Ed explains Medicare Secondary Payer
Video coming soon
I'm recording a walkthrough of the MSP rules — the working-aged twenty-employee rule, the disability one hundred-employee rule, the thirty-month ESRD coordination period, and what happens when there's a workers' comp settlement or a car accident. Drop your email below and I'll send it the day it goes live.
Which of these sounds more like you?
MSP situations look different depending on what other coverage you have. Pick the one that sounds most like you.
I'm 65+, still working, employer has 20 or more employeesEmployer plan pays first; Medicare pays second
Under 42 CFR § 411.172, your employer's group health plan is primary and Medicare is secondary. The 20-employee threshold counts current and preceding-calendar-year employees on at least 20 calendar weeks (§ 411.170(a)(2)(i)).
File claims with the employer plan first. Medicare can pay the secondary share against deductibles and coinsurance up to the limits in 42 CFR § 411.33. You don't have to drop the employer plan — in most cases, you shouldn't.
I'm 65+, working, employer has fewer than 20 employeesMedicare is primary; employer plan pays second
Small employers (under 20 employees) are not subject to the working-aged MSP rule. Medicare pays first; the employer plan is secondary or wraparound. This is a meaningful enrollment trap — if you delayed Part B because you assumed your employer plan was primary, you may owe a Part B late enrollment penalty.
If your employer is part of a multi-employer plan that includes at least one large employer, the large-employer rule may still apply; check with the plan administrator and CMS COB&R.
I'm under 65 on Medicare via disability, employer has 100+ employeesLarge group health plan pays first; Medicare second
Under 42 CFR § 411.204 and § 411.102(c), a Large Group Health Plan (100 or more employees) of an employer covering you or a family member with current employment status pays primary; Medicare pays secondary.
The LGHP is forbidden by § 411.108 from "taking into account" your Medicare entitlement — they cannot drop you, raise your premiums, cut benefits, or steer you onto Medicare-first.
I'm on Medicare for End-Stage Renal Disease and have an employer planGroup plan primary for the first 30 months; Medicare second
ESRD has its own MSP timeline. The group health plan (any size) pays primary during a coordination period of 30 months that starts when you become Medicare-eligible based on ESRD. After 30 months, Medicare flips to primary.
The group plan cannot "take into account" ESRD-based Medicare eligibility, and cannot differentiate against ESRD enrollees (§ 411.102(a)). Your kidney pages and the dialysis-or-transplant page on this site cover the rest of the timeline.
I had a workers' compensation injuryWorkers' Comp pays first for related care
Under 42 CFR § 411.40, Medicare does not pay for services that workers' compensation has paid for, can reasonably be expected to pay for, or would have paid for if you had filed a proper claim. WC is primary for the work-related injury; Medicare is primary only for unrelated care.
If your WC settlement includes future medical care, a Workers' Comp Medicare Set-Aside (WCMSA) may need to be funded — that money has to be exhausted on related care before Medicare pays for the related condition (42 CFR § 411.46).
I had a car accident or filed a liability claimAuto/no-fault/liability primary for accident-related care
Under 42 CFR § 411.50, no-fault auto and liability insurance are primary for care related to the accident. Medicare may make a conditional payment if the liability insurer won't pay promptly (within 120 days), but Medicare must be reimbursed from any settlement or judgment (§ 411.24(h) — within 60 days of receipt).
Report pending liability and no-fault cases to the CMS Coordination of Benefits and Recovery Center early. CMS will issue a conditional-payment summary statement and, after settlement, a recovery demand letter.
I'm helping a parent or spouse sort out who pays firstWhat you'll need before you call CMS or SHIP
Before you pick up the phone, gather: their Medicare card (HICN/MBI), employer plan card, employer name and approximate size, dates of any recent accidents, any open WC claim numbers, VA enrollment status if a veteran, TRICARE status if active-duty connected, and any pending liability case attorney name.
The Medicare Coordination of Benefits & Recovery Center at 1-855-798-2627 will speak to a representative if there's an authorization on file. A SHIP counselor can sit on a call with you and the family member — free, confidential, and trained on MSP. Find local SHIP at 1-877-839-2675.
My situation is something elseVA, TRICARE, Federal Black Lung, or a multi-coverage stack
MSP gets technical when more than two payers are involved or when federal programs (VA, TRICARE, Federal Black Lung) are in the mix. General rules: VA pays for service-connected care directly; TRICARE coordinates with Medicare under separate DoD/CMS rules; Federal Black Lung pays primary for related conditions (42 CFR § 411.40(b)(1)(ii)).
For anything outside the standard working-aged / disability / ESRD / WC / auto-liability fact patterns, call the CMS Coordination of Benefits & Recovery Center at 1-855-798-2627 or a SHIP counselor at 1-877-839-2675. They handle the unusual stacks every day.
Everything people ask me about MSP
When is Medicare the primary payer?
Medicare is primary when no other payer is responsible first. Common scenarios: you're retired and have only Medicare; your employer has fewer than 20 employees (working-aged rule); you're past the 30-month ESRD coordination period; or any care unrelated to a workers' comp injury, auto accident, or liability case. The reverse — Medicare as secondary — is the more complicated and more common-trip-up situation.
When does Medicare pay second?
Medicare is secondary when another payer is responsible first. The five most common triggers: (1) you're 65+ and your employer has 20 or more employees; (2) you're under 65 with disability-based Medicare and your employer has 100 or more employees; (3) the first 30 months of ESRD-based Medicare; (4) workers' compensation paying for a work-related injury; (5) auto/no-fault/liability paying for accident-related care.
How does the 20-employee rule actually count employees?
Under 42 CFR § 411.170(a)(2)(i), an employer is treated as having 20 or more employees if it had 20 or more employees on each working day in each of 20 or more calendar weeks in the current calendar year or the preceding calendar year. Affiliated companies are aggregated under the IRC section 52 and 414(m) rules in 42 CFR § 411.106. So a part-time-heavy small company can still cross the threshold, and a chain of related companies can be aggregated.
If I'm on disability Medicare and my spouse has employer coverage, who pays first?
If you're under 65 on Medicare based on disability and you're covered under your spouse's employer plan based on the spouse's current employment status, the LGHP rule applies if the spouse's employer has 100 or more employees. The plan pays first and Medicare pays second. If the employer is smaller, Medicare is primary.
What is a Workers' Comp Medicare Set-Aside (WCMSA) and do I need one?
A WCMSA is the portion of a workers' comp settlement designated to pay for future Medicare-covered medical care related to the injury. The WCMSA must be exhausted on related care before Medicare will pay for that condition (per 42 CFR § 411.46). CMS reviews WCMSA proposals over certain thresholds; the most current review thresholds and the WCMSA Reference Guide are published on cms.gov. If you're settling a WC claim, talk to a workers' comp attorney before signing.
I had a car accident. Will Medicare pay my medical bills?
Auto no-fault and liability insurance are primary for accident-related care under 42 CFR § 411.50. If the auto insurer won't pay promptly (within 120 days), Medicare may make a conditional payment — but Medicare must be repaid from any settlement or judgment within 60 days under § 411.24(h). Report the case to the CMS Coordination of Benefits & Recovery Center early so conditional-payment tracking starts on day one.
What is the MSP questionnaire and do I have to answer it?
The Medicare Secondary Payer questionnaire (sometimes called the Initial Enrollment Questionnaire) is a CMS form asking about all your other coverage. CMS uses it to figure out who pays first for your claims. Yes, you have to answer it. Failure to respond is a top reason claims get denied or delayed — the system literally cannot tell who pays first without your answers.
Will Medicare ever pay before VA?
VA and Medicare don't coordinate the way two civilian insurers do. The VA generally pays for care delivered at VA facilities or by VA-authorized providers; Medicare generally pays for care from civilian providers Medicare contracts with. For service-connected conditions, the VA is the primary payer. There's no traditional "primary/secondary" coordination on the same claim — you choose where to get care.
Does TRICARE coordinate with Medicare?
Yes. Once you become entitled to Medicare Part A, you generally need to enroll in Part B to keep TRICARE — the program then becomes TRICARE for Life, which acts as wraparound coverage with Medicare paying first for Medicare-covered services and TRICARE paying second. The exact rules vary by status (active duty, retiree, family member); confirm with your TRICARE Regional Contractor and the COB&R Center.
Where do I get help with a complicated MSP situation?
Two free resources. (1) CMS Coordination of Benefits & Recovery Center: 1-855-798-2627 — the official CMS hotline for MSP questions, conditional-payment information, and recovery cases. (2) SHIP (State Health Insurance Assistance Program) at 1-877-839-2675 — free, unbiased counseling on Medicare and MSP, with counselors trained on the working-aged, disability, ESRD, and WC/auto/liability fact patterns.
Other programs that interact with Medicare
Medicare doesn't live alone. If you have other coverage now, or you're checking on benefits a parent or spouse may also qualify for, here are the programs that most often coordinate.
Working past 65 with employer coverage
If you're 65 or older, still working, and your employer has 20 or more employees, the employer plan pays first and Medicare pays second. The Working-Past-65 page walks through Part B enrollment timing and the Special Enrollment Period when your employer coverage ends.
COBRA and Medicare
COBRA continuation coverage is treated differently than active-employment coverage. When COBRA is the only other coverage, Medicare is generally primary. If you may qualify for COBRA after losing employer coverage, the COBRA-and-Medicare page explains how the order changes.
Medicare and ESRD (kidney failure)
If you may qualify for Medicare based on End-Stage Renal Disease, your group health plan is primary for the first 30 months and Medicare flips to primary after that. The ESRD page covers the eligibility timeline and how this coordination period interacts with COBRA.
Late Enrollment Penalty (LEP)
Skipping Part B because you assumed an employer plan was primary — when it wasn't — is a top reason people end up with a Part B late enrollment penalty. If you may have an LEP issue tied to a small-employer or COBRA situation, the LEP page covers appeals and recalculation.
Medicaid + Medicare (dual eligible)
Medicaid is generally the payer of last resort — it pays after Medicare, after employer coverage, and after WC/auto/liability. If you may qualify for both Medicare and Medicaid, the dual-eligible page explains how the two programs coordinate and what Medicare Savings Programs cover.
VA health care
VA and Medicare don't coordinate the way two civilian payers do. VA pays VA providers; Medicare pays civilian providers. If you may qualify for both, the VA-and-Medicare page covers when each one is the right card to hand the front desk.
Help me keep my MSP guide current.
The thresholds, statutes, and CMS guidance change. If you want me to email you when something material moves on Medicare Secondary Payer rules, drop your email and I'll keep you posted.
Visual placeholder only. This staging build does not submit data. No spam. I'll only email when something on this page actually changes.