• The Bornhätter-Ferguson method is an actuarial method for calculating losses to estimate their ultimate amount. The amount of expected unreported losses (obtained using the reciprocal of the loss development factor (LDF)) is added to the actual reported losses to arrive at the estimated final loss for that year of the incident. This method is most useful when actual reported losses in the year of the incident are a poor indicator of future incurred but not reported (IBNR) losses in the same year of the incident, as is often the case when the loss rate is low but very high. potential severity.