Excess kurtosis compares the kurtosis coefficient with that of a normal distribution. Since normal distributions have a kurtosis of three, excess kurtosis can be calculated by subtracting kurtosis by three. Thus, a kurtosis of more than 3.0 will have positive excess kurtosis and be leptokurtic, with relatively fat tails and skinny center. If there is instead a kurtosis of less than 3.0, you have negative excess kurtosis, resulting in a platykurtic distribution with smaller tails and a broader center.