A quarter of pensioners (25%) are unaware they could increase their state pension income by filling in gaps in their National Insurance (NI) record, new research has revealed. A further 10% of those aged 66 or over were unsure, according to retirement specialist Just Group which said the findings are a clear reminder that people should check their NI history before claiming the state pension.

Figures from the Department for Work and Pensions show of the 4.5 million pensioners receiving the new state pension, 45% (around 2 million) are currently not getting the full entitlement (£11,973 for this tax year). The data also shows 200,721 new state pension claimants receive less than 50% of the full amount. To claim the full new state pension, at least 35 years of qualifying NI contributions are required, with at least 10 qualifying years needed in order to receive any new state pension payment.

Just Group says gaps in NI records can be backfilled by “paying for voluntary Class 3 National Insurance contributions”, although this can only be done for the previous six tax years.

According to MoneyWeek, for each year someone buys, they get an extra 1/35ths state pension which could add up to an additional £340 a year.

Just Group added NI credits can also be claimed for reasons such as maternity leave, unemployment, sickness or for providing caring responsibilities to fill gaps.

Its research found that less than 60% of those of the state pension age or older knew how many years’ worth of NI contributions are needed to claim the full amount.

Stephen Lowe, from Just Group, said: “Millions of people do not receive the full amount because they have not built up enough qualifying years of National Insurance contributions.

“Before people claim the State Pension, we’d urge them to check if they will actually receive the full nSP (new state pension) and if not to review their NI record to see where they have gaps in their record.

“For some, it may make sense to pay extra to make the contributions voluntarily and retrospectively for the previous six tax years. The extra income over the course of a retirement may offset the initial cost of these contributions.

“For others who may have spent time out of the workforce on maternity leave or providing care for loved ones, for example, they may be eligible to claim NI credits which can help fill in gaps and build extra state pension income for free.

He added: “The Government provides a range of free resources to help people understand the rules and available help as well as the options for their specific circumstances.”

Research by Just Group also revealed how much pensioners rely on their state pension.

It found 13% of over 66s said the state pension accounted for more than 90% of their monthly household income, with 44% saying it represented more than of their household income.