Underwriting is the process by which an insurer evaluates the risk of insuring a person or asset and decides whether to accept it, modify it, refer it, or decline it, and on what terms. The typical underwriting process includes collecting applicant information, classifying the risk, evaluating hazards, applying rating plans, credits, and debits, deciding whether to accept, modify, refer, or decline, and finally issuing the policy and binding coverage, sometimes through a temporary binder. For life insurance, underwriters weigh factors such as age, gender, health status, family medical history, occupation, lifestyle choices like smoking or alcohol use, hobbies such as aviation or extreme sports, and the type and amount of coverage requested. Property underwriters focus on location, construction type, age of building, occupancy, fire protection availability, security measures, prior claims history, and exposure to natural hazards. Underwriting guidelines codify acceptable risks and referral thresholds to ensure consistency across the team. A declination occurs when a risk falls outside the insurer's appetite; the applicant may then seek coverage in a non-standard or specialty market.
Once a risk is classified, premium calculation follows a clear hierarchy. The pure premium equals the expected losses per exposure unit, calculated as total expected losses divided by the number of exposure units, and represents only the cost of claims. The risk premium adds a margin for uncertainty, capital costs, and profit. The net premium covers expected benefits and risk costs, while the gross premium adds expense loading for administration, commissions, taxes, contingencies, and profit. Underwriting profit loading and contingency loading ensure the insurer collects enough premium beyond expected losses to remain solvent and profitable. Expected losses themselves combine loss frequency and loss severity, since the expected pure premium equals \(frequency \times severity\). Variance of collective risk measures how much total losses of an entire pool might deviate from expected totals, and shrinks as pool size grows. A credit-based insurance score, derived partly from credit history, is also used by many insurers to predict claim likelihood.
Several rating methods bring these pieces together. Manual rating uses a published rate manual based on class-level characteristics rather than the insured's own claim history. Retrospective rating determines the final premium after the policy period based on actual losses incurred, subject to minimum and maximum premium limits. Schedule rating adds or subtracts debit or credit percentages for individual risk characteristics not captured in the manual. Experience rating and prospective rating adjust premiums based on the insured's own past loss history, with credibility theory blending an insured's experience with manual rates by assigning a credibility factor Z between 0 and 1. A premium audit verifies estimated exposure bases after the policy period, while burning cost is a similar historical method applied to reinsurance treaties and large commercial risks. The exposure base must correlate strongly with potential losses. A trend factor adjusts historical data to current or future cost levels. Finally, a homogeneous risk pool groups exposures with similar loss characteristics, which improves pricing accuracy while permitting some heterogeneity for risk spreading.