Description: On July 1 1997, a new privatized but compulsory retirement system came into effect in Mexico. The new system has a complex web of contributions by employers, employees and by the government. The retirement funds also have a complex web of charges applied to the funds. This paper carefully analyzes these complex cases to find out which funds perform the best. It shows through simulations that the optimal strategy for individual retirement account holder is not to stay with one fund throughout the working life. Instead, the best option is to switch at some point. The switching point depends on a number of factors: 1. the wage rate of the workers [and also on the growth rate of wages], 2. the real interest rate, and 3. the inflation rate. From Actuarial Research Clearing House 1999, Vol. 1.