Only a third of individuals (33 per cent) are receiving the full new state pension, according to analysis from Canada Life.
A freedom of information request from the pension provider showed that almost two in five pensioners - 365,290 people or 38 per cent of claimants - received less than £150 a week, while 282,447 pensioners (29 per cent) are receiving more.
Under the new system, announced in 2014, pensioners currently receive £168.90 a week but the data from the Department for Work and Pensions were presented in rounded figures.
The state pension flat rate is also tied to a triple lock, meaning it is uprated by the higher of average earnings growth, the consumer price index, or 2.5 per cent.
People are eligible for the full state pension if they have paid full-rate national insurance contributions for at least 35 years, compared to the previous threshold of 30 years.
People can receive less than the full flat rate state pension when their national insurance record is incomplete or they have paid in for fewer than the 35 qualifying years required under the new rules (usually through periods of contracting out).
But people can also receive more if they have a ‘protected payment’, as benefits built up over the old and new system are worth more than the new flat rate, Canada Life stated.
Andrew Tully, technical director at Canada Life, said the state pension is the foundation of most people’s retirement plans, and yet the data showed more than half of those eligible to claim the state pension under the new flat rate system receive less than the full amount.
He said: "Given the various changes that have been introduced over the years, it’s not surprising people find the whole system difficult to understand.
"The state pension can be a minefield but ask for a forecast of what you are likely to receive and mind any contribution gaps.
"And remember, it is only really there to provide a basic standard of living when you retire. Take control and seek professional advice if you plan to make the most of your retirement."
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