New analysis has shown that around 150,000 pensioners were on less than £100 a week.
Royal London said that 1,737,342 of 3,407,567 people receiving the new pension received the full weekly amount last year.
It made the calculations using Department for Work and Pensions (DWP) data from spring 2023.
The full state pension for 2024/25 is £221.20 a week, up from £203.85 last year.
In general, to get the pension people need to have 35 years of national insurance contributions (NICs). Those with fewer “qualifying” years receive a proportionately smaller state pension.
Royal London found that 149,317 pensioners who had reached state pension age from April 2016 were receiving a state pension of less than £100 a week – and 17,546 pensioners were receiving less than £20 a week.
It also said that 5,677 people were receiving less than £10 a week.
The new state pension system was introduced in 2016 to provide a sustainable, clear foundation pension for people to build their private savings on.
Many people will have other sources of income alongside the state pension, such as workplace or private pensions.
Pensioners on low incomes may be entitled to claim pension credit, which can top up their incomes and the Department for Work and Pensions (DWP) recently launched an awareness drive to boost take-up.
While around 1.4 million pensioners are already receiving pension credit, there are up to an estimated 880,000 households eligible for the support who are yet to claim.
Around 10 million pensioners are set to lose out on winter fuel payments as the new Government restricts the benefit to only those receiving pension credit.
The move was announced by the Government as part of a package of measures designed to tackle a £22 billion “black hole”.
Sarah Pennells, consumer finance specialist at Royal London, said: “We often talk about the full state pension amount, but these figures show how many pensioners are getting only a fraction of that.
“One of the main reasons why people miss out on the full state pension is because they have gaps in their national insurance record, but they may not realise this until it’s too late to do anything about it.
“You may have national insurance gaps because, for example, you were working but had low earnings, were unemployed but didn’t claim benefits, were a high earner with young children who didn’t register for child benefit, or because you were working abroad.
“The good news is that, even if you have gaps in your national insurance record going back over a decade or more, it may still be possible to top up your national insurance contributions and increase the amount of state pension you’re entitled to.
“Under the new state pension system, you don’t get any state pension at all if you have fewer than 10 years’ national insurance, so it’s important to check your national insurance contribution record.”
A DWP spokesperson said: “Ensuring a better deal for the pensioners of today and tomorrow is a priority for this Government.
“There are a variety of reasons why some pensioners have a lower state pension – including contracting-out and paying less national insurance contributions – which is why we encourage those on the lowest incomes to claim for pension credit, worth on average £3,900 per year.
“Through our commitment to protect the triple lock over 12 million pensioners will benefit, with many expected to see their state pension increase by around a thousand pounds over the next five years.”
