The average maturity of the index is the weighted average of the remaining life of senior debt instruments in the index.

The higher the average maturity, the longer it takes for the debt instruments in the index to reach maturity.

\text{Average maturity}_{t} = \frac{\sum\limits_{i=1}^{n} (M_{i,t} \times w_{i,t})}{\sum\limits_{i=1}^{n} w_{i,t}} |

where:

M_{i,t} is the weighted average maturity of debt instruments of constituent i at time t

w_{i,t} denotes weight of constituent i at time t