Male life expectancy is much higher than originally estimated, leading pension researchers have said.
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The Pensions Policy Institute (PPI) said life expectancy for unskilled and professional men has been understated.
Life expectancy at birth is 71 years for a manual worker and 79 years for a professional - a gap of eight years.
But if measured at age 65 instead, the PPI said, a manual worker will live to 81 years and a professional worker to 86 years - a gap of just five years.
The PPI's estimate is higher because it excludes people who have died before they reach 65 years of age and also takes into account ongoing improvements in life expectancy.
The government has ruled out raising the state pension age, because it says it would penalise lower-skilled workers who generally have lower life expectancies.
Chris Curry, PPI research director, said its calculations suggested there could be more pressure on state pension spending than originally envisaged.
"Even people in social class V [unskilled manual workers] who are widely likely to have the lowest life expectancy can still expect to live 16 years after state pension age," he said.
Researchers have not updated life expectancy projections for women, who on average live longer than men.