Catastrophe PML Calculator
Probable maximum loss (PML) is a key risk metric for property insurers, reinsurers, and risk managers. It estimates the largest loss likely to result from a single catastrophic event under normal protection conditions. This calculator applies a damage factor (the percentage of total insured value expected to be destroyed in the worst credible event) and a concentration factor (the share of the total portfolio exposed to the same event) to estimate portfolio PML. For single-location analysis, the concentration factor is 1.0. For a geographic portfolio, enter the percentage of total insured value in the concentrated zone.
PML formula
Exposed TIV = TIV x Concentration factor
PML = Exposed TIV x Damage factor
The concentration factor represents the share of the portfolio exposed to a single catastrophic event. The damage factor represents the percentage of exposed value expected to be destroyed. Both are expressed as decimals (e.g. 60% = 0.60).
PML in insurance underwriting and reinsurance
- Underwriters compare the per-risk PML to the insurer's net retention limit. If PML exceeds the retention, reinsurance is needed.
- Catastrophe models (AIR, RMS, CoreLogic) produce probabilistic PML estimates at various return periods (1-in-100 year, 1-in-250 year).
- For wind hurricane, damage factors range from 5 to 40 percent for engineered structures depending on zone; for direct landfall scenarios, 50 to 80 percent is possible.
- Fire PML for a single building with suppression: typically 10 to 25 percent of replacement value.
- Earthquake PML for California high-rise: commonly modelled at 10 to 30 percent of insured value using probabilistic seismic hazard analysis.
Catastrophe PML: frequently asked questions
What is probable maximum loss (PML)?
Probable maximum loss (PML) is the estimated maximum loss that could reasonably be expected from a single catastrophic event, given normal operating conditions and all fire and disaster protection systems functioning. It is expressed as a dollar amount or percentage of the total insured value. PML is used for risk management, reinsurance purchasing, and solvency assessment.
How is PML different from maximum foreseeable loss (MFL)?
PML assumes that protection systems (sprinklers, fire walls) function normally, limiting the loss. MFL assumes protection systems fail, representing the worst-case scenario. PML is the standard underwriting metric; MFL is used for worst-case stress testing. PML is typically 30 to 60 percent of MFL for well-protected properties.
What damage factors are used for different perils?
Damage factors vary significantly by peril and construction type. For fire, typical PML factors are 10 to 25 percent for fire-resistive construction with sprinklers, 25 to 50 percent for ordinary construction, and up to 75 percent without fire protection. For earthquake in high-risk zones (California), PML factors of 10 to 30 percent of replacement value are common.
How does geographic concentration affect PML?
A concentration factor accounts for the correlation of losses across an insured portfolio when multiple locations are exposed to the same catastrophic event (hurricane, earthquake). A single isolated building has no concentration risk; a portfolio of buildings in the same flood zone has very high concentration risk.
Who uses PML calculations?
Property underwriters use PML to set per-risk limits and pricing. Reinsurance buyers use portfolio PML to purchase catastrophe excess-of-loss coverage. Risk engineers assess individual location PML. Regulators and rating agencies use aggregate PML to assess insurer solvency against catastrophe scenarios.
Official sources
- NAIC: NAIC Consumer Resources.
- Federal Insurance Office (US Treasury): FIO Annual Report on the Insurance Industry.
Reviewed by the CalculatorHub team, edited by James Graham, 15 June 2026. See our methodology.