Concept Architecture
Concept
Theoretically, Coinsurance Rate is the predetermined proportion of eligible healthcare costs that an insured individual is required to pay after any applicable deductible has been satisfied. It defines the degree of financial risk shared between the insurer and the insured and is a fundamental parameter in health insurance benefit design. The concept is grounded in insurance economics and actuarial science, where proportional cost sharing is used to balance financial protection with incentives for efficient healthcare utilisation.
Mathematically, the Coinsurance Rate is represented as a proportion or percentage applied to the eligible cost of healthcare services. The patient's financial responsibility equals the product of the coinsurance rate and the covered healthcare cost, while the insurer pays the complementary proportion. The rate therefore determines the allocation of expenditure between the two parties.
In practice, coinsurance rates are specified within health insurance contracts and commonly range from 10% to 30% for covered services, although values vary by jurisdiction and benefit design. Actuarial models use the coinsurance rate when estimating expected insurer liabilities, patient out-of-pocket expenditure, premiums and actuarial value. The rate remains in effect until any policy-specific out-of-pocket maximum has been reached.
Purpose
Used to determine the proportion of healthcare costs paid by insured individuals, allocate financial responsibility between patients and insurers, support insurance benefit design, estimate expected healthcare expenditure and model patient cost-sharing.
Mathematical Formulae
Primary Formula
Coinsurance Rate = Patient Payment � Eligible Healthcare Cost
Supporting Formulae
Patient Payment = C ? r
Insurer Payment = C ? (1 ? r)
where:
- C = eligible healthcare cost
- r = coinsurance rate
Related Mathematical Methods
- Proportional cost allocation
- Actuarial modelling
- Risk-sharing models
- Expected value analysis
- Insurance benefit modelling
Example
A patient receives a covered hospital service costing �4,000 after satisfying the deductible. The insurance policy specifies a coinsurance rate of 25%.
Patient Payment = �4,000 ? 0.25 = �1,000
Insurer Payment = �4,000 ? 0.75 = �3,000
The patient's coinsurance rate is therefore 25%, resulting in a �1,000 out-of-pocket payment.
Excel Implementation
| Function | Example Formula | Health Economics Application |
|---|---|---|
| Division | =B2/C2 | Calculates the coinsurance rate from patient payment and eligible cost. |
| PRODUCT | =B2*C2 | Calculates the patient's coinsurance payment from the service cost and coinsurance rate. |
| PRODUCT | =B2*(1-C2) | Calculates the insurer's payment. |
| IF | =IF(B2>D2,B2*C2,0) | Applies coinsurance after deductible requirements have been met. |
VBA (Optional)
A VBA routine can automatically apply policy-specific coinsurance rates to healthcare claims and calculate patient and insurer payment obligations.
Sources
- Dickson DCM, Hardy MR, Waters HR. Actuarial Mathematics for Life Contingent Risks.
- Zweifel P, Breyer F, Kifmann M. Health Economics.
- Cutler DM, Zeckhauser RJ. The Anatomy of Health Insurance.
- Drummond MF, Sculpher MJ, Claxton K, Stoddart GL, Torrance GW. Methods for the Economic Evaluation of Health Care Programmes.
- ISPOR Good Practice Reports.
Related Concepts (2)
Library
Publications
1
The Economics of Health and Health Care — Folland, Goodman, Stano & Danagoulian, 9th Edition ed., 2024 (Routledge)
The market-leading general health economics textbook, giving comprehensive coverage of health economics through core economic themes and balancing theory, empirical evidence and public policy. The ninth edition adds chapters on health disparities and pandemic economics.
BookView source →
Frequently Asked Questions (6)
What is a coinsurance rate?
The specific percentage of a covered service's cost an insured person is responsible for paying under a coinsurance arrangement.
Source: Cutler DM, Zeckhauser RJ. The anatomy of health insurance. In: Culyer AJ, Newhouse JP, eds. Handbook of Health Economics. Vol 1A. Elsevier; 2000:563-643. doi:10.1016/S1574-0064(00)80170-5.
What percentage does a coinsurance rate specify?
A coinsurance rate is the specific percentage of a covered service's cost that the insured is responsible for paying under a coinsurance arrangement. It fixes the split between patient and insurer, so a rate of twenty percent means the patient pays a fifth of the cost and the insurer the rest. A higher rate shifts more of the cost onto the patient, raising what they pay for any given service, and it is the number that puts coinsurance into effect. The patient's set share of a cost is what it specifies. Cutler and Zeckhauser (2000) set out the anatomy of insurance.
Source: Cutler & Zeckhauser 2000
How does a coinsurance rate work?
A coinsurance rate works by setting the percentage of a covered service's cost the insured pays, so applying the rate to the cost gives the enrollee's share, with the insurer paying the rest. So a coinsurance rate works by fixing the percentage share, which is why it determines the enrollee's payment, since the rate applied to the cost gives what they pay, and a coinsurance rate sets the specific percentage of a covered service's cost the insured is responsible for under the coinsurance arrangement.
Source: Cutler & Zeckhauser 2000
What does the coinsurance rate determine?
The coinsurance rate determines the share of a covered service's cost the insured pays, so a higher rate means the enrollee pays a larger percentage and a lower rate a smaller percentage. So the coinsurance rate determines the enrollee's percentage share, which is why it matters, since it sets how much of the cost they bear, and the coinsurance rate determines the specific percentage the insured pays under coinsurance, fixing their share of a covered service's cost while the insurer pays the remainder.
Source: Cutler & Zeckhauser 2000
What does a higher coinsurance rate mean?
A higher coinsurance rate means the insured pays a larger percentage of a covered service's cost, so the enrollee bears more of the cost and the insurer pays less. So a higher coinsurance rate means more cost for the enrollee, which is why the rate matters, since it sets the share they pay, and a higher coinsurance rate means the insured is responsible for a larger percentage of the covered service's cost, increasing their share under the coinsurance arrangement.
Source: Cutler & Zeckhauser 2000
How does the coinsurance rate relate to coinsurance?
The coinsurance rate relates to coinsurance as the percentage it uses: coinsurance is the arrangement of paying a percentage of cost, and the coinsurance rate is the specific percentage the insured pays. So the coinsurance rate defines the coinsurance share, which is why they are connected, since the rate sets how much of the cost the enrollee bears, and the coinsurance rate is the percentage applied under coinsurance, determining the insured person's share of a covered service's cost.
Source: Cutler & Zeckhauser 2000
Trust Record
Verified by Dr Darrin Baines
British health economist
Professional identity: darrinbaines.org
Verification date: 12 Jan 2026
Content version: 1.0.0
Canonical Identity
- Persistent URI
- https://healtheconomics.wiki/concept/coinsurance-rate
- Term code
- HS-HP-HI-039
Stable URI · Machine-readable · Resolvable · CC BY 4.0