Workers who think they have excellent chances of living to ages 75 and 85 plan to work longer than those who think their chances are poor, according to a new study by the Center for Retirement Research at Boston College.

With life expectancy of 65 having increased dramatically in the past few decades, longevity has sharply increased the time spent in retirement, said the researchers.

And with Social Security and employer pension plans replacing a smaller share of earnings for retirement at any age, working longer has become increasingly essential to secure an adequate income in later years,

The study, “Do Longevity Expectations Influence Retirement Plans?” released this month, also showed that perceptions of life expectancy influence workers’ actual retirement behavior as well as their plans, though to a lesser degree.

Overall, subjective life expectancy has a substantial and statistically significant effect on retirement.

These results are consistent with the notion that while workers who expect to live longer plan to retire later, actual retirement plans are influenced by unexpected shocks, the research concluded.