How to Calculate Deductible and Coinsurance, With 16 Worked Examples

How to Calculate Coinsurance in 4 Steps

1. Find the allowed amount. This is the price your plan accepts, often lower than the billed charge.
2. Take off the deductible you still owe. You pay that part in full.
3. Multiply what is left by your coinsurance rate. On an 80/20 plan your rate is 20%.
4. Add the two parts. Then check the total against your out-of-pocket maximum.

The 16 examples below use these steps. Many come from the kinds of questions asked in insurance licensing, medical billing and personal finance classes.

Deductible First, Then Coinsurance

Example 1: $500 deductible, 80/20 coinsurance, $1,500 bill

Question: A plan has a $500 deductible and 80/20 coinsurance. The deductible has not been met. How much does the patient pay on a $1,500 bill?

1. Deductible first: the patient pays $500.
2. What is left: $1,500 − $500 = $1,000.
3. Coinsurance: 20% of $1,000 = $200.
4. Total: $500 + $200.

Answer: The patient pays $700. The plan pays $800.

Example 2: $500 deductible, 80/20 coinsurance, $2,000 bill

Question: A patient has a $500 deductible and 80/20 coinsurance. The bill is $2,000 and none of the deductible has been met. What does the patient owe?

1. Deductible: $500.
2. What is left: $2,000 − $500 = $1,500.
3. Coinsurance: 20% of $1,500 = $300.

Answer: The patient owes $800. The plan pays $1,200.

Example 3: $624 bill, 80% coverage, $150 deductible

Question: Your medical bill is $624. Your plan covers 80% after a $150 deductible. How much will you pay?

1. Deductible: $150.
2. What is left: $624 − $150 = $474.
3. The plan covers 80%, so your share is 20% of $474 = $94.80.

Answer: You pay $244.80. The plan pays $379.20.

Example 4: $2,345 bill, 70% coverage after a $120 deductible

Question: Your medical bill is $2,345. Your insurance covers 70% after a $120 deductible. What amount will you pay?

1. Deductible: $120.
2. What is left: $2,345 − $120 = $2,225.
3. The plan covers 70%, so your share is 30% of $2,225 = $667.50.

Answer: You pay $787.50. The plan pays $1,557.50.

Example 5: $10,100 hospital bill, $100 deductible, 80/20

Question: A patient is in the hospital for 3 days and gets a bill for $10,100. The major medical policy has a $100 deductible and 80/20 coinsurance. How much is the patient responsible for?

1. Deductible: $100.
2. What is left: $10,100 − $100 = $10,000.
3. Coinsurance: 20% of $10,000 = $2,000.

Answer: The patient pays $2,100. The plan pays $8,000.

Example 6: Part of the deductible is already met

Question: A plan has a $1,000 deductible and 20% coinsurance. The patient has already paid $400 toward the deductible this year. What do they owe on a $3,000 bill?

1. Deductible left: $1,000 − $400 = $600.
2. What is left of the bill: $3,000 − $600 = $2,400.
3. Coinsurance: 20% of $2,400 = $480.

Answer: The patient owes $1,080. The plan pays $1,920.

No Deductible, or Deductible Already Met

Example 7: 70/30 plan, $660 emergency room bill

Question: An insurance policy pays 70/30. An emergency department bill is $660. What amount will the patient have to pay?

1. No deductible is mentioned, so coinsurance applies to the whole bill.
2. The patient share is 30% of $660 = $198.

Answer: The patient pays $198. The plan pays $462.

Example 8: Deductible already met, 80/20, $175 bill: what does the insurer pay?

Question: A major medical plan has 80/20 coinsurance and a $75 deductible. The insured has already met the deductible and gets a bill for $175. How much will the insurer pay?

1. The deductible is met, so skip it.
2. The insurer pays 80% of $175 = $140.
3. The patient pays the other 20%: $35.

Answer: The insurer pays $140. Read the question twice: this one asks for the insurer's share, not the patient's.

Example 9: Deductible just met, $1,000 lab bill

Question: A member recently met their deductible. How much is the coinsurance on a $1,000 bill for lab work?

1. The deductible is met, so only coinsurance applies.
2. With 20% coinsurance: 20% of $1,000 = $200.
3. With 30% coinsurance: 30% of $1,000 = $300.

Answer: The answer is $200 at 20% or $300 at 30%. Use the coinsurance rate given in the member's plan details.

Example 10: Comparing a deductible policy with a coinsurance policy

Question: One policy has a $600 deductible. Another has 20% coinsurance and no deductible. The bill is $4,000. How much does the patient pay under the coinsurance policy?

1. Coinsurance policy: 20% of $4,000 = $800.
2. Deductible policy, for comparison: the patient pays the $600 deductible.

Answer: Under the coinsurance policy the patient pays $800, which is $200 more than under the $600 deductible policy.

Copay Examples

Example 11: $30 copay, $220 office visit

Question: Your plan has a $30 copay for in-network doctor visits. The total cost of the visit is $220. How much will you pay?

1. A copay is a flat fee. It does not depend on the size of the bill.

Answer: You pay $30. The plan covers the other $190.

Example 12: $25 copay, $185 follow-up visit

Question: You pay a $25 copay whenever you visit your doctor. A follow-up visit comes to $185. What is your share of the cost?

1. The copay is fixed at $25, whatever the bill is.

Answer: Your share is $25. The plan covers $160.

Example 13: Prescription copay when the deductible does not apply

Question: A patient has a $250 deductible with none of it met. The drug has a $45 copay, and the deductible does not apply to this drug. What does the patient pay for the first fill?

1. The deductible does not apply to this drug, so ignore the $250.
2. Only the copay is due.

Answer: The patient pays $45.

Allowed Amounts, Out-of-Pocket Maximums and Small Bills

Example 14: Billed $75, allowed $68, plan pays 80%

Question: A patient is seen for an office visit billed at $75. The policy pays 80% of the allowable amount, which is $68. What is the patient responsibility?

1. Coinsurance uses the allowed amount, not the billed charge.
2. The plan pays 80% of $68 = $54.40.
3. The patient pays 20% of $68 = $13.60.
4. An in-network provider writes off the other $7 ($75 − $68).

Answer: Collect $13.60 from the patient.

Example 15: When the out-of-pocket maximum stops the math

Question: A plan has a $2,000 deductible, 20% coinsurance and a $5,000 out-of-pocket maximum. Nothing has been paid yet this year. What does the patient owe on a $40,000 hospital bill?

1. Deductible: $2,000.
2. Coinsurance: 20% of $38,000 = $7,600.
3. Without a cap that would be $9,600.
4. The out-of-pocket maximum is $5,000, so the patient stops there.

Answer: The patient owes $5,000. The plan pays $35,000.

Example 16: The bill is smaller than the deductible

Question: A plan has a $1,500 deductible and 20% coinsurance. Nothing has been paid toward the deductible. What does the patient owe on a $400 bill?

1. The whole $400 goes toward the deductible.
2. No coinsurance yet, because the deductible is not met.
3. Deductible still left for the year: $1,500 − $400 = $1,100.

Answer: The patient owes the full $400.

Tips for Exam and Homework Questions

• Check who the question asks about. "How much will the insurer pay" and "how much will the patient pay" have different answers.
• 80/20 means the plan pays 80% and you pay 20%. "Covers 70%" means your share is 30%.
• Look for "has met the deductible". If it is met, skip straight to coinsurance.
• A copay question usually has a trick. The size of the bill does not matter. The copay is the answer.
• Use the allowed amount when the question gives both a billed charge and an allowed amount.

Check Your Own Numbers

For a real bill, use our coinsurance calculator, which also handles out-of-pocket maximums, or the patient responsibility calculator for a full estimate. See also deductible vs copay vs coinsurance, what the allowed amount is and the 2027 out-of-pocket maximums.

Frequently Asked Questions