A statistical method of estimating outstanding claims, whereby the weighted average of past claim development is projected into the future. The projection is based on the ratios of cumulative past claims, usually paid or incurred, for successive years of development. It requires the earliest year of origin to be fully run-off or at least that the final outcome of that year can be estimated with confidence. It appropriate, the method can be applied to past claims data that have been explicitly adjusted for past inflation.