Commercial insurance underwriters use probable maximum loss (PML) calculations to estimate the highest maximum claim that a business most likely will file, versus what it could file, for damages resulting from a catastrophic event. Although underwriters use complex statistical formulas and frequency distribution charts, the concepts involved are not difficult to understand. In fact, once you understand the basic PML formula, you can estimate your own PML and use this information as a starting point in negotiating favorable commercial insurance rates.

1. Calculate the Value of Business Property

Calculate the dollar value of business property to establish the amount you stand to lose if a catastrophic event demolished your business. If you already have business property insurance, this is the amount of insurance coverage. Otherwise, add real property and business personal property to reach the valuation.

2. Identify Risk Factors

Identify risk factors that increase the chance a specific catastrophic event would demolish your business. For example, risks associated with a fire include combustible construction materials, clutter, flammable liquids or other substances used to operate or maintain your business, and distance to the nearest fire station. Risks associated with flooding include the business site, such as whether you are in a documented flood plain, construction materials and storage policies.

3. Identify Risk Mitigation Factors

Identify risk mitigation factors that decrease the chance a specific catastrophic event would demolish your business. For example, risk mitigation factors associated with a fire include functioning protection systems such as alarms, automatic sprinklers and portable fire extinguishers. Also, consider elements in your emergency action plan that address emergency reporting procedures and policies for protecting business assets.

4. Conduct a Risk Analysis

Conduct a risk analysis to estimate the degree to which risk mitigation factors decrease the chance a catastrophic event will demolish your business. The difference between these two factors determines the maximum loss your business is likely to incur. Insurance companies typically use percentages that increase incrementally by 1 percentage point. For example, an analysis might determine that risk mitigation decreases the chance of a total loss by 21 percent.

5. Calculate the Probably Maximum Loss

Multiply the property valuation by the highest expected loss percentage to calculate the probable maximum loss. For example, if the property valuation is $500,000 and you determine that fire risk mitigation reduces expected losses by 20 percent, probable maximum loss for a fire is $500,000 multiplied by .80 or $400,000.


Contact your insurance agent for help in assessing risk and risk mitigation factors. For a specific event, such as a fire, contact your local fire station or inspector for assistance.


Don’t expect the amount you calculate to match an insurance company’s PML calculation. In fact, even insurance companies often vary widely in PML calculations, primarily due to differences in how insurance companies view and weigh risks and risk mitigation factors.