Credibility-Weighted Premium Calculator

Credibility is the weight given to a risk's own loss experience versus a broader manual or class rate. A credibility factor Z between 0 and 1 blends the two: the credibility-weighted premium is Z times the experience premium plus (1 minus Z) times the manual premium. More data earns more credibility.

A common approach is limited fluctuation (classical) credibility using the square-root rule: Z equals the square root of the number of claims divided by the full-credibility standard, capped at 1. The full-credibility standard is the claim count at which experience is given full weight. This calculator uses that square-root method.

The full-credibility standard is the number of claims (or exposures) at which a risk's own experience is considered fully credible, so Z equals 1. A frequently cited benchmark is 1,082 claims for a 90 percent probability of being within 5 percent, but the standard depends on the chosen confidence and tolerance, so it is a user input.

A single risk's experience is volatile when claim counts are low, so relying on it alone produces unstable rates. The manual rate reflects a larger, more stable pool. Credibility weighting takes the responsiveness of own experience and the stability of the manual rate in proportion to how much data supports the experience.

No. More claims raise the credibility factor Z, shifting weight toward the risk's own experience. Whether the blended premium rises or falls depends on whether that experience premium is above or below the manual premium. Credibility controls the weight, not the direction.