The population forecast conducted by Statistics Netherlands is the starting point for the calculation of the future number of centenarians. The forecast only predicts the number of persons aged 99 years or older. In order to estimate the number of centenarians, the proportion of people aged 100 or more was calculated in the group of people aged 99 and older for the period 1990-2010. These proportions turn out to be fairly consistent over the years; 56% for men and 58% for women. The calculation is based upon the forecast of the number of over-99s and the hypothesis that the proportions of men and women among centenarians will not change.