In a recent pension fund valuation, which involved splitting the fund between two groups of members in proportion to the net liabilities, the writer found that he had to calculate a large number of annuity values for a variety of ages between 60 and 80 at several rates of interest with guarantee periods ranging from 1 to 10 years. In view of the nature of the valuation a broad adjustment was not good enough, and the problem arose of how to reduce the calculations to a minimum and yet retain an acceptable degree of accuracy in the approximation. It is thought that an account of the method which was evolved may be of interest and of use to readers of the Journal.