What's the difference between a copay and coinsurance?

A copay is a flat dollar amount you pay for a specific service. Coinsurance is a percentage of the total cost you pay after meeting your deductible. Both are forms of cost-sharing where you and the insurance company split the bill, but the structure is fundamentally different.

Copay (copayment):

• Fixed dollar amount: $20, $50, $250, etc.
• Predictable — you know the cost before the service
• Usually applies AFTER deductible is met (sometimes before, depending on plan)
• Common for: PCP visits, specialist visits, ER visits, urgent care, prescriptions

Example: $30 copay for a primary care visit. You pay $30, plan pays the rest.

Coinsurance:

• Percentage of the Medicare-approved or insurance-allowed amount
• Variable — depends on the actual cost of the service
• Typically applies AFTER deductible is met
• Common for: hospital stays, surgery, advanced imaging (MRI, CT), durable medical equipment, specialty drugs

Example: 20% coinsurance on outpatient surgery that costs $5,000. After meeting your deductible, you pay $1,000 (20% of $5,000), plan pays $4,000.

Side-by-side comparison:

| Service | Copay structure | Coinsurance structure |
|---|---|---|
| Primary care visit ($150 cost) | $30 copay = $30 | 20% coinsurance after deductible = up to $30 |
| Specialist visit ($300 cost) | $50 copay = $50 | 20% = $60 |
| MRI ($2,500 cost) | Often subject to coinsurance | 20% = $500 |
| Outpatient surgery ($8,000 cost) | Rarely flat copay | 20% = $1,600 |
| Hospital stay ($25,000 cost) | Sometimes a per-admission copay | 20% = $5,000 |
| Generic prescription ($10 retail) | $0–$5 copay | Rarely coinsurance |
| Specialty drug ($3,000/month) | Sometimes copay | Often 25%–33% coinsurance = $750–$990 |

Why this matters for plan choice:

Copay-heavy plans (more predictable):
- Easier to budget — you know the cost of routine services
- Better for people who use predictable amounts of care (regular doctor visits, multiple prescriptions)
- Common in HMO Medicare Advantage and Gold/Platinum ACA plans

Coinsurance-heavy plans (less predictable, often lower premium):
- Lower monthly premium typically
- Higher exposure for major events (surgery, hospital, advanced imaging)
- Common in Bronze and Silver ACA plans, some PPO plans

Real-world example — same cancer treatment, different plan structures:

A $50,000 chemotherapy regimen:

Plan A (copay-heavy): $5,000 deductible, $300 copay per chemo visit, $1,500 copay per inpatient admission
- Year 1 cost: deductible $5,000 + 12 chemo copays = $3,600 + 1 hospitalization $1,500 = $10,100

Plan B (coinsurance-heavy): $5,000 deductible, 30% coinsurance on chemo and hospital, $9,200 OOP max
- Year 1 cost: deductible $5,000 + 30% of remaining $45,000 = $13,500 → caps at OOP max $9,200

In this case, Plan B caps your exposure at the OOP max, while Plan A's copays alone might let you exceed the OOP max if there are many visits. Both plans cap your maximum at the OOP max — but the path there differs dramatically.

Specialty drug coinsurance trap:

The biggest gotcha for many seniors is specialty drug coinsurance on Medicare Part D and ACA plans. Specialty drugs (cancer treatments, multiple sclerosis, autoimmune conditions, biologics) are often Tier 4 or Tier 5 with 25–33% coinsurance.

Example: $3,000/month specialty drug at 33% coinsurance = $1,000/month copay × 12 months = $12,000/year.

With the new 2026 Part D $2,000 OOP cap, this is no longer a catastrophic disaster — once you hit $2,000 in covered drug spending, you pay $0. But for people NOT on Medicare (under 65 ACA), specialty drug coinsurance can still be devastating up to the medical OOP max.

How to compare plans on copay vs coinsurance:

1. For each plan, list the cost-sharing for the services YOU actually use:

1. Calculate total annual cost = (premium × 12) + deductible (if you'll meet it) + sum of expected copays/coinsurance

1. Compare across plans: the lowest premium isn't always the cheapest total cost.

1. Always check the OOP max — that's your worst-case scenario in a high-cost year. Lower OOP max = better protection.

Glossary recap:

• Premium: What you pay monthly to have insurance (regardless of whether you use it)
• Deductible: What you pay first, before insurance pays anything for most services
• Copay: Flat dollar amount per service (e.g., $30 PCP visit)
• Coinsurance: Percentage of cost per service after deductible (e.g., 20% of MRI cost)
• Out-of-pocket maximum (OOP max): The most you'll pay total in a year for covered services
• Premium does NOT count toward deductible or OOP max

What to do next: Call (866) 534-1886. We calculate total annual cost on every plan in your ZIP based on YOUR specific services and prescriptions — so the cheapest premium doesn't trick you into a more expensive total cost. Free.