Underinsurance Calculator & Guide

Determine the financial impact of being underinsured. This calculator shows the payout you would receive based on your policy’s coinsurance clause if your property is not insured to its full required value.

Estimated Insurance Payout

$0.00

---

What is the Formula Used to Calculate Underinsurance?

Underinsurance occurs when a property is insured for less than its true value, creating a coverage gap. Most commercial and many homeowner’s insurance policies include a “coinsurance” or “average” clause to address this. This clause penalizes the policyholder for not maintaining adequate coverage. The formula used to calculate underinsurance payout is designed to ensure policyholders bear a proportional share of the loss if they haven’t paid for sufficient coverage. Understanding this formula is crucial for anyone looking at a hypothetical example of an insurance claim.

This principle protects insurers from clients who might intentionally underinsure a property, paying a lower premium while expecting full coverage for any partial loss. The core idea is that if you insure only 60% of your property’s value, the insurer should only be responsible for 60% of any loss.

The Underinsurance Formula and Explanation

When a claim is filed on an underinsured property, the payout is not simply the amount of the loss. Instead, it is adjusted based on the degree of underinsurance. This adjustment is often referred to as a coinsurance penalty.

The standard formula is:

Payout = (Amount Insured / Required Insurance) x Amount of Loss

This payout amount cannot exceed the Amount Insured. It’s a key part of risk management to review your policy for clauses like this. For further reading, see our guide on the What is a Coinsurance Clause?

Variables in the Formula

Variable	Meaning	Unit	Typical Range
Amount Insured	The coverage limit you purchased for the property.	Currency ($)	Varies based on property value.
Required Insurance	The property’s actual value multiplied by the coinsurance percentage. (e.g., $500,000 value * 80% = $400,000 required).	Currency ($)	Typically 80% or 90% of the property’s value.
Amount of Loss	The financial damage incurred that needs to be repaired or replaced.	Currency ($)	From $0 up to the total value of the property.

Practical Hypothetical Examples

Example 1: Sufficiently Insured Property

Imagine your property is correctly valued and insured.

• Inputs:
  • Actual Property Value: $1,000,000
  • Amount Insured For: $850,000
  • Coinsurance Requirement: 80%
  • Amount of Loss: $150,000
• Calculation:
  • Required Insurance: $1,000,000 x 80% = $800,000.
  • Since the Amount Insured ($850,000) is greater than the Required Insurance ($800,000), no penalty applies.
• Result:
  • The insurer pays the full Amount of Loss (minus any deductible). Payout = $150,000.

Example 2: Underinsured Property (Hypothetical Example)

Here is a hypothetical example where the property owner is underinsured and faces a penalty.

• Inputs:
  • Actual Property Value: $1,000,000
  • Amount Insured For: $600,000
  • Coinsurance Requirement: 80%
  • Amount of Loss: $150,000
• Calculation:
  • Required Insurance: $1,000,000 x 80% = $800,000.
  • The Amount Insured ($600,000) is less than the Required Insurance. The penalty formula applies.
  • Payout = ($600,000 / $800,000) x $150,000 = 0.75 x $150,000 = $112,500.
• Result:
  • The insurer pays only $112,500. The policyholder is responsible for the remaining $37,500 of the loss. This demonstrates the impact of the formula used to calculate underinsurance. You can learn more about valuing your property in our Property Valuation Guide.

How to Use This Underinsurance Calculator

1. Enter Actual Property Value: Input the current, full replacement cost of your property.
2. Enter Amount Insured For: Provide the coverage limit from your insurance policy.
3. Set Coinsurance Requirement: Adjust the percentage to match your policy’s clause (usually 80% or 90%).
4. Enter Amount of Loss: Input the cost of the damage you are claiming.
5. Click “Calculate”: The tool will show your estimated payout, any penalty, and the amount you’re responsible for. The results help visualize the formula used to calculate underinsurance.

Key Factors That Affect Underinsurance

• Inflation: Rising construction and material costs can quickly increase your property’s replacement value, making your coverage obsolete.
• Renovations and Improvements: Adding a new room or upgrading a kitchen increases property value, requiring an update to your insurance limit.
• Inaccurate Initial Valuation: Basing coverage on market value or purchase price instead of rebuild cost is a common error. See our comparison of Actual Cash Value vs. Replacement Cost.
• Forgetting Other Structures: Failing to include fences, sheds, garages, or driveways in the total property value.
• Ignoring Professional Fees: The cost to rebuild should also account for architects, surveyors, and debris removal fees.
• Not Reviewing Annually: Insurance needs change. An annual review is the best way to prevent becoming underinsured. Our Home Insurance Calculator can assist with this.

Frequently Asked Questions (FAQ)

1. What is the ‘average clause’ in insurance?

The ‘average clause’ is another term for the coinsurance clause. It dictates that if you are underinsured, you must share in the loss with the insurer, proportional to the amount of underinsurance.

2. Does underinsurance apply to a total loss?

In a total loss scenario, the underinsurance formula is less relevant. The insurer will pay out the maximum limit of your policy (the “Amount Insured For”), and you are responsible for the rest. For example, if your $1M home is insured for $600k and is a total loss, you get $600k.

3. How can I avoid being underinsured?

Get a professional appraisal for your property’s replacement cost, review your policy and coverage limits annually, and inform your insurer of any significant upgrades or renovations.

4. Is market value the same as replacement cost?

No. Market value is what your property would sell for, including land. Replacement cost is the price to rebuild the structure from scratch. Always use replacement cost for insurance.

5. What does a coinsurance percentage of 80% mean?

It means you must insure your property for at least 80% of its total replacement value to avoid a financial penalty on partial loss claims. This is a common requirement in many policies.

6. Why does my policy have a coinsurance clause?

It encourages policyholders to insure their property to its true value, ensuring fair premium payments relative to the risk the insurer is taking on.

7. Does this formula apply to all types of insurance?

The formula used to calculate underinsurance is most common in property insurance (both residential and commercial). It is less common in auto or liability insurance.

8. What if my loss is smaller than my deductible?

If the loss is smaller than your deductible, you would not file a claim as the entire cost would be your responsibility. Your deductible is the amount you pay before insurance coverage begins.