Less than half of those reaching state pension age between 2016 and 2020 will be entitled to a full new state pension, it has been revealed.

About 3.5 million workers will reach their state pension age between 2016 and 2020 but, out of these, only 45% will be entitled to a full new state pension of at least £148.40, pensions firm Hargreaves Lansdown has said. This will mean about two million retiring pensioners will get less than the full amount.

The current means-tested state pension, which is made up of a basic payment and top-ups linked to career earnings, is set to be replaced with a single payment of at least £148.40 in today's money in April 2016.

People who reach pensionable age after April 2016 will see their national insurance contributions count towards a "single tier" amount.

But a freedom of information request submitted by Hargreaves Lansdown has revealed that just 45% of those retiring between 2016 and 2020 are set to receive the full state pension amount.

Who is affected?

The majority of people falling short of the full state pension are likely to have been contracted out during their working lives. Others who get less than 100% are likely to be those with interrupted National Insurance contribution histories, such as mothers and the self-employed.

Tom McPhail, head of pensions research at Hargreaves Lansdown, says: "The new state pension will ultimately be a simpler and fairer system.

"However, in the short term it will be complicated and many people are likely to get less than they may expect."

He adds that, with new pension freedoms meaning that people will be able to spend all their private pension savings, it is imperative that workers receive a proper state pension forecast. (See our State Pensions guide for more on getting a forecast.)

McPhail says: "Without this, they could get a nasty shock when they do reach state pension age."

What does the Government say?

The Department for Work and Pensions (DWP) insists that no one would lose out as a result of the changes and many people would be better off.

While contracting out is being abolished – meaning that payments will become increasingly similar over time – the DWP says that it had always made clear that the differences could not be eliminated overnight.

A DWP spokesman says: "Language about people 'missing out' is utterly misleading.

"Those retiring when the new state pension is in place will get at least what they would have got for the NI contributions they have paid in the current system, and many will get more.

"Our historic pension reforms will create a simplicity that hasn't existed in decades, giving people a greater sense of economic security and peace of mind in retirement.

"The new state pension will tackle inequalities of the past, with women, carers, lower earners and the self-employed set to benefit the most."