The object of this note is to suggest a method, believed by the writer to be new, whereby once a pension fund contribution has been calculated the revised contribution occasioned by a small change in the rate of interest can be approximately determined with great ease and rapidity.

Let 100cx be the percentage contribution for entry age x required to support a pension per annum equal to 100k % of pensionable salary for each year of service. Assume for simplicity that normal retirements and early retirements (if any) can together be sufficiently allowed for by the use of a single average retirement age (M).