The authors have developed an econometric growth model to estimate an “optimal” diversification of wages. Pay disparities are optimal when they produce the highest rate of GDP growth. An optimal diversification of wages can be calculated by introducing a variable thanks to which the model will measure “parabolic” disparities. The authors advance a hypothesis that there is an optimal level for the diversification of wages. If pay disparities are smaller than optimal, the most creative, hard-working and efficient individuals are insufficiently rewarded and are not properly encouraged to take advantage of their capabilities in contributing to gross domestic product. If wage disparities are greater than optimal, employees with lower qualifications are underpaid. This can be accompanied by feelings of social injustice and a sense of exploitation and impoverishment. This harms interpersonal ties and the relationship between employees and employers, in addition to limiting people’s confidence and reducing social capital. In such a situation, low-paid employees have little incentive to work. They only have enough motivation to satisfy their minimum biological needs and stay above the poverty line. Underpaid employees display insufficient creativity and dedication. The empirical analysis conducted by the authors for the Polish economy applies to the 1986-2004 period. The analysis shows that pay disparities are higher than optimal and have grown steadily since 1999. A statistically significant slowdown in productivity caused by an excessive diversification of wages occurred in 2003 and 2004. At the time, productivity dropped by around 0.5 and 0.8 percentage points respectively.