The impact of aggregate mortality risk on defined benefit pension plans

We calculate the risk faced by defined benefit plan providers arising from uncertain aggregate mortality - the risk that the average participant will live longer than expected. First, comparing the widely cited Lee-Carter model to industry benchmarks that are commonly employed by plan providers, we show that these benchmarks appear to substantially underestimate longevity. The resultant understatement of liabilities may reach 12.2% for typical male participants in defined benefit plans and may reach 22.4% for male workers aged 22. Next, we consider consequences for plan liabilities if aggregate mortality declines unexpectedly faster than is predicted by a putatively unbiased projection. There is a 5% chance that liabilities of a terminated plan would be 3.1% to 5.3% higher than what is expected, depending on the mix of workers covered.