Health insurance doesn’t pay all of your health care expenses. Instead, you’re expected to foot the bill for part of the cost of your care through your health plan’s cost-sharing requirements like your deductible, copayments, and coinsurance.

Since deductibles and copayments are fixed amounts, it doesn’t take a lot of math to figure out how much to pay. A $30 copayment to fill a prescription or see a doctor will cost you $30 no matter how much the total bill for the prescription or office visit was.

Your health insurance picks up the rest of the tab (note that this generally only applies if you use an in-network provider and fulfill any prior authorization requirements that your insurance plan has).

However, calculating your health insurance coinsurance payment is trickier. Since coinsurance is a percentage of the total cost for the service, you’ll owe a different amount of coinsurance for each service you receive.

If the health care service you received was cheap, your coinsurance won’t be much. However, if the health care service was expensive, your coinsurance could wind up being hundreds or even thousands of dollars (on the high end, your coinsurance will be limited by your health plan's maximum out-of-pocket).

You need to understand how to calculate your health insurance coinsurance payment so you’ll know how much you’ll owe for coinsurance and you can budget for it.

Find Your Coinsurance Rate

You’ll need to find your coinsurance rate for the type of care you’re getting. You should be able to locate this in the Summary of Benefits and Coverage you got when you enrolled in your health plan. Sometimes you can even find it on your health insurance card.

Be careful; in some health plans, coinsurance can be the same percentage no matter what type of service you get. For example, 30% coinsurance for hospitalization and 30% coinsurance for specialty drug prescriptions.

In other health plans, you might have a low coinsurance rate for some services and a higher rate for other types of services. For example, you could have 35% coinsurance for hospitalization, but only 20% coinsurance for surgery at an outpatient surgery center.

And it's very common for prescription drug coverage to be structured with copayments for drugs that are in lower-cost tiers, but coinsurance for higher tier or specialty drugs. So you may be accustomed to paying a flat dollar amount at the pharmacy, but then end up having to pay a percentage of the cost of a new prescription—which can get quite expensive, depending on the drug.

Find the Cost of Your Care

Once you know your coinsurance rate, you need to determine the total cost of the health care service you received. If you’re using an in-network provider, your health plan has already negotiated discounts from that provider.

Calculate your health insurance coinsurance payment based on the discounted rate, not the standard rate charged to people who don’t belong to your health plan.

Find this in-network discounted amount on your Explanation of Benefits (EOB) listed as “allowed amount" (the EOB will also show the amount the provider billed, which will generally be higher than the allowed amount).

If you haven’t gotten the healthcare service yet, you won’t have an EOB to check. You can try asking your medical provider or health insurer what the in-network rate for that particular service is.

But know that sometimes you simply won't be able to get an accurate estimate of the total cost of your treatment in advance, either because the information is considered proprietary (as part of the network negotiations between the insurer and the medical provider) or because the medical provider won't know in advance exactly what services need to be performed.

The Trump administration has finalized a health care transparency rule that will be phased in starting in 2022 (and fully in force by 2024), requiring health plans to make pricing and network-approved costs available to consumers upon request.

This rule is controversial, with insurers deriding it as unnecessary and costly (it is expected to result in lower MLR rebates, as well as higher premiums in the individual/family health insurance market), while HHS officials herald it as a big step forward for health care price transparency.

A similar, but much less far-reaching rule was finalized in 2019, requiring hospitals to publicize their network-negotiated rates for common services. This rule is being challenged in court but will take effect in January 2021 if it's not overturned.

If the care you're going to need is a basic service that doesn't vary from case to case (an MRI, for example), the hospital or doctor's office should be able to give you a total price in advance.

But if you're having a surgical procedure, the doctor may not know exactly what will be involved until they actually do the surgery—and no amount of transparency regulations can address that.

You can rest assured that your health plan's maximum out-of-pocket will kick in if the bill becomes substantial, but if your out-of-pocket maximum isn't met, the amount you'll have to pay in coinsurance could be subject to change.

Calculate Your Coinsurance

To calculate the coinsurance you owe, you’ll first convert your percentage figure into a decimal figure by moving the decimal point two spaces to the left like this:

Now, multiply this decimal figure by the network-approved amount for the service you had or will have. Note that this is not the same as the amount that is billed by the medical provider since insurance companies negotiate lower rates and require their in-network medical providers to write off the portion of their bill above that amount.

Assuming you've used an in-network medical provider, the coinsurance amount is calculated based on the network-approved price, NOT the amount that was initially billed.

Coinsurance rate (as a decimal figure) x total cost = coinsurance you owe.

Examples

Follow these two examples to see the calculations and results

Antoine

Antoine’s health plan requires 20% cost-sharing to fill a prescription. The network-negotiated price for his prescription is $150.

0.20 x $150.00 = $30.00
Coinsurance rate x total cost = coinsurance Antoine owes.

Antoine owes $30 coinsurance for this particular prescription.

Kinsey

Kinsey’s health plan requires 35% cost-sharing for hospitalizations. The total network-negotiated cost for her hospital stay, after she pays her deductible, is $12,850.00

0.35 x $12,850 = $4,497.50
Coinsurance rate x total cost = coinsurance Kinsey owes.

Kinsey will owe $4,497.50 in coinsurance charges for her hospitalization, in addition to the amount of her deductible (that's assuming she hasn't yet met her health plan's out-of-pocket maximum yet).

Factors Affecting Coinsurance Amount

Don’t forget that you must also pay your deductible. On some health plans, you’ll have to pay the entire deductible before your health plan begins to pay part of the cost of your non-preventive care. Only after you’ve paid your full deductible will you be sharing the cost of your care with your health plan by paying coinsurance.

If you have a really big health care bill, your out-of-pocket maximum might kick in and protect you from some of the cost. Once the deductibles, copayments, and coinsurance you’ve paid this year add up to the out-of-pocket maximum, your cost-sharing requirements are finished for the year.

Your health plan picks up 100% of the cost of your covered in-network care for the rest of the year. You don’t have to pay coinsurance, copays, or deductibles again until next year (usually). Note that this isn't how it works with Medicare.

Thanks to the Affordable Care Act, most preventive care must be covered by your health insurance without requiring coinsurance, copayments, or even a deductible, as long as your health plan isn't grandfathered.

This means you won’t have to pay coinsurance on things like your yearly physical exam, yearly mammogram, and routine immunizations. Although it may seem like preventive care is free, it’s not. Instead, the cost of that preventive care is included in your monthly health insurance premium whether or not you actually use the care.

It's also important to note that while some of these services, such as mammograms and colonoscopies, are fully paid for by your health insurance without cost-sharing if they're done on a preventive basis, but subject to your deductible and coinsurance if they're considered diagnostic.

So if you're just going in for your routine annual mammogram, you won't have to pay anything. But if you've found a lump in your breast and are having a mammogram to determine whether it's cause for concern, expect to have to pay your health plan's normal cost-sharing (deductible and/or coinsurance) for the mammogram.