Expectation of life calculates the average age at which someone will die. Conventionally it’s calculated from birth, but can be calculated from any given age. For pensioners the measure often given most prominence is expectation of life at age 65, ie how many years the pensioner could, on average, expect to survive after retirement.
The report by the IFS also asked those who had thought about how long their retirement would be to name a figure. But the average expectation was 20.6 years at age 65, implying an average life expectancy of 83.3 years, which is younger than suggested by actuarial life tables.