Most modern life tables have “forced”
termination. Forced termination means that the last row of the life
table applies for all persons with ages on or after the last age in
the life table.

This sample illustrates forced termination.

In this case, the last row of the life table applies for all
persons aged 100 or older. Specifically, *q*_{x} probabilities
are _{1}*q*_{x} for
ages less than 100 and, technically, _{∞}*q*_{x} for
age 100.

Forced termination has terminal age values that apply to all
ages after the terminal age so that `lx`

is positive, `qx`

is `1`

,
and `dx`

is positive. Ages after the terminal age
are `NaN`

values, although `lx`

and `dx`

can
be `0`

and `qx`

can be `1`

for
input series. Forced termination is triggered by a naturally terminating
series, the last age in a truncated series, or the first `NaN`

value
in a series.