Probable maximum loss
Risk · Cloudbreak team · Updated October 29, 2026 · 8 sources
Definition
Probable maximum loss (PML) is the amount of loss tied to a stated chance of being exceeded over a set period, often given as a return period such as 100 or 250 years.1,2,3 In property loss control, PML has an older, site-level meaning: the maximum loss expected at one location from a fire there, in dollars or as a percentage of total values.4
How it works
A PML has two parts: an amount and a probability. A 100-year occurrence PML of $6 million means a 1-in-100 (1%) chance in a year of a loss of at least $6 million.2
The return period is the reciprocal of the probability: 1 / 100 is 1.0% and 1 / 250 is 0.4%. It is an average, not a schedule. A 100-year loss can happen in back-to-back years or not for centuries.2,3
Catastrophe models simulate many years of possible storms or earthquakes against a portfolio or a single property and rank the results on an exceedance probability (EP) curve. A PML is read off that curve on one of two bases. Occurrence (OEP) uses the largest single event in a year. Aggregate (AEP) adds up every event in the year.5,3
PML is not the worst possible loss. Rarer events cause larger losses, so a PML only means something with its probability attached. In the site-level loss control sense, it is a judgment about one building's fire exposure rather than a modeled probability.
Example
The Academy ran a hypothetical book of 100,000 Florida homes through a catastrophe model. Each home had a $207,500 building value and a 2% deductible.2
| 100-year (1.0%) | 250-year (0.4%) | |
|---|---|---|
| Hurricane wind | 1,315 | 1,902 |
| Inland flood | 202 | 384 |
| Storm surge | 97 | 157 |
| Tornado and straight-line wind | 37 | 52 |
| All causes combined | 1,458 | 2,031 |
PMLs do not add up. The four 100-year PMLs sum to $1,651 million, but the combined 100-year PML is $1,458 million, because the chance that every peril has its 1-in-100 year at once is far below 1%. Average annual losses, by contrast, do add up.2
A reinsurance layer from the 100-year to the 250-year hurricane wind PML covers $587 million ($1,902 million minus $1,315 million). Losses reach it with a 1.0% probability and use it up with a 0.4% probability.2
PML also tells apart sites that look alike on average. Two Florida locations, in ZIP codes 32053 and 32311, had similar hurricane wind AALs ($98.16 and $91.88) but 250-year PMLs of $5,024.54 and $6,025.14, or 51 and 66 times AAL.2
Where you'll see it
- Insurer risk limits and reinsurance: an insurer may set a limit such as $100 million of loss likely to be exceeded only once in 100 years and check it against its EP curve. Return periods help set reinsurance attachment and exhaustion points.1,3
- Lender due diligence: seismic reports for multifamily loans in high seismic areas, covered in the next section.6,7
Lender rules: earthquake loss in loan reviews
Fannie Mae requires a seismic risk assessment for a property with a listed structural risk factor in a high seismic risk area. The assessment must meet ASTM E2026 and ASTM E2557 (the standard practice for PML evaluations) and estimate the Scenario Expected Loss (SEL) and Scenario Upper Loss (SUL) using a 10% chance of exceedance in 50 years.6
Freddie Mac uses SEL-475 in place of the older term PML: the mean loss from a 475-year return period earthquake, as a percentage of current building replacement cost.7
Fannie Mae accepts an SEL of 20% or less when ASTM E2026 building stability is met, and a lender may not deliver a loan if any improvement's SEL is above 40%. For example, on a building with a $20,000,000 replacement cost, a 15% SEL is a $3,000,000 mean loss, while 25% is $5,000,000, above the 20% line.6,7
Questions
- What does a 1-in-100 PML mean?
- There is a 1% chance each year of a loss at least that large. It does not mean the loss happens once every 100 years.2,3
- Is PML the worst possible loss?
- No. It is the loss at a chosen probability, and rarer events cause larger losses. In the Academy's example the 250-year hurricane PML, $1,902 million, is 45% above the 100-year PML of $1,315 million.2
- What is the difference between PML and average annual loss?
- Average annual loss is the average loss across all simulated years, which equals the pure premium. PML is a single loss at a set probability, out in the tail of the curve.3
Cloudbreak
Cloudbreak keeps every policy, statement of values and loss run in one place per property, tracks renewals, and watches every building against storms with its proprietary predictive storm engine, built with AI and backed by meteorologists.
Sources
Written by the Cloudbreak team. Numbers, dates and rules cite the published sources below.
- 1. American Academy of Actuaries, Catastrophe Management Work Group: Insurance Industry Catastrophe Management Practices (June 2001)
- 2. American Academy of Actuaries, Extreme Events and Property Lines Committee: Uses of Catastrophe Model Output (July 2018)
- 3. National Association of Insurance Commissioners (NAIC): NAIC Catastrophe Modeling Primer (adopted August 13, 2025), Attachment Three to Executive (EX) Committee and Plenary minutes
- 4. International Risk Management Institute (IRMI): IRMI Glossary: Probable Maximum Loss (PML)
- 5. National Association of Insurance Commissioners (NAIC): Catastrophe Models (Property)
- 6. Fannie Mae: Multifamily Selling and Servicing Guide, Part II Section 505: Seismic Risk (effective October 26, 2026)
- 7. Freddie Mac: Multifamily Seller/Servicer Guide, Chapter 64: Seismic Risk Assessment Requirements
- 8. National Association of Insurance Commissioners (NAIC): Calculation of Catastrophe Risk Charge Rcat (PR027), year-end 2024 RBC instructions extract