Since 1999 the pension benefit in Brazilian Social Security System is calculated by multiplying the average 80% higher earnings by the Social Security Factor (SSF). This factor is an Automatic Balancing Mechanism, that can be understood as a Notional Defined Scheme. The formulation of SSF takes into consideration contribution years, social security tax rate, age and life expectancy at the retirement year. The formulation also presents a gender differentiation, by adding five contributory years for women. Although this formula is based on actuarial fundamentals (i.e., the higher the contributory period, the higher the value of the benefit), it has been extremely criticized. At least three important changes have been analyzed in the congress. The first one is Rule 85/95 (the sum of age and contributory years must be at least 85 for women and 95 for men). The second proposal is to eliminate the SSF. And the third proposed change is to compute the earnings average using only the last 36 months in the labor market. Based on this scenario, the paper has two objectives. The first is to evaluate the actual formulation and the three proposals using four parameters largely adopted in the social security literature: Replacement Rate, Internal Rate of Return, Effective Rate and Actuarially Fair Rate. The second objective is to calculate the Actuarially Fair Social Security Factor (what should be the SSF values to be classified as actuarially fair) and compare it with the SSF. The results show that the current formula penalizes (encourages) the workers who retire early (in late ages) in a more than actuarially fair way, according to the four criteria. The actual system is also progressive and strongly benefits women of all ages, compared to men. All proposals are more generous than the current rule, what raises strong doubts about their adequacy.