The weighted average maturity is also called the weighted average life. It is a measure of how quickly principal will be repaid according to the bond's debt service structure.
To find the average weighted life, the number of bond years is divided by the number of bonds. Bond years are the amount of principal maturing in each year multiplied by the number of years to maturity and divided by $1,000. Similarly, the number of bonds is the total principal divided by $1,000.
Weighted average maturity = bond years / number of bonds