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Home > Insurance Markets Checklists > Understanding and Calculating Probable Maximum Loss (PML)

Insurance Markets Checklists

Understanding and Calculating Probable Maximum Loss (PML)

Checklist Description

This checklist describes what probable maximum loss is and how it is calculated.

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Probable maximum loss (PML) is a term chiefly used in the insurance industry. PML is the anticipated value of the biggest monetary loss affecting a business and/or a building that could result from a catastrophe, whether natural or otherwise, called for this purpose a “maximum credible event” (buildings are considered separately by insurers as the owner may be different from the owner(s) of any businesses contained therein). For example, the catastrophe could be a hurricane, floods, or other severe weather event, or other disaster that has a given probability of occurrence within a stated time period (such as the loss of a building and the value of the business contained therein as a result of fire). PML is usually expressed as a percentage of the total value, experienced by a structure or collection of structures when subjected to a maximum credible event. The PML is usually smaller than the maximum foreseeable loss (MFL), which assumes that all protective features fail, resulting in a complete write off. For example, in a fire this would include such things as failure of the sprinkler systems in the building. Underwriting decisions are typically influenced by the evaluation of the PML. The amount of reinsurance for a known risk is also normally based on the valuation of the PML. PML and MFL are both calculated as the percentage of a building or business that under normal conditions could be damaged or destroyed in a single event. The calculation takes into account variables such as construction of the building, susceptibility of the contents (including the value of any business), and protection measures. The MFL calculation also includes failures of key loss reduction systems in place (for example, sprinkler systems failing to activate in the case of a fire).

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  • Consistent, accurate estimates of PML and MFL help to understand the extent of the risk involved, analyze the hazards and potential losses in order to manage them better, assess economic losses, determine the amount of reinsurance, and satisfy any reinsurance requirements.

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  • Calculating PML and paying for the resulting insurance may not be viable in geographic areas that are typically subject to natural disasters such as earthquakes or hurricanes. It may be cheaper, instead, to purchase business continuity insurance to cover for such losses caused by fire or other destruction.

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Action Checklist

  • Carry out a risk assessment before calculating the PML, to reduce insurance costs. The information gleaned from this can be used to assist the insured to develop long-term strategies for risk reduction. Such strategies could include upgrading buildings and equipment, developing better operating procedures, transferring risk through insurance, and improving emergency response and business recovery plans.

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Dos and Don’ts


  • Take a practical and logical approach that covers all important aspects of a maximum credible event, such as damage to structures, equipment and inventory, business interruption costs, and the safety of staff.


  • Don’t underestimate the potential amount of downtime your business may experience if hit by the kind of loss covered by PML.

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Further reading


  • Grace, Martin Francis, Robert W. Klein, Paul R. Kleindorfer, and Michael R. Murray. Catastrophe Insurance: Consumer Demand, Markets and Regulation. Boston, MA: Kluwer Academic, 2003.
  • Grossi, Patricia, Howard Kunreuther, and Chandu C. Patel. Catastrophe Modeling: A New Approach to Managing Risk. New York: Springer, 2005.
  • Messy, Flore-Anne. Catastrophic Risks and Insurance. Policy Issues Series. Paris: OECD Publishing, 2005.


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