More than half of pensioners failed to claim £687 worth of state benefits they were entitled to in 2013, according to an equity release specialist.
Some 41% of Just Retirement's clients didn't claim any of the state support they qualified for, while 13% didn't take advantage of their full entitlement, the firm said.
Nearly two-thirds were eligible for at least one state benefit but only a fifth of them claimed all they could. Three in five didn't claim anything at all and one-in-five under-claimed.
While the average amount of lost income was just shy of £60 a month, Just Retirement highlighted the case of one client who failed to claim an extra £3,244 a year, or £62 a week.
The number of people failing to claim any entitlement doubled between 2012 and 2013, from 23 to 41%. The amount of income they stood to lose also rose, from just under £650 to around £770.
Over the period, while the number of clients identifying that they were entitled to more state help fell from 33 to 13%, the amount they were failing to claim rose by almost 75% from £212.97 to £372.53.
Peace of mind
Just Retirement spokesperson Stephen Lowe said: "The economy may be picking up but these figures suggest more than half of pensioners might not be taking every step they can towards making ends meet."
He added: "Many are missing out on hundreds of pounds a year that could make a real difference to their standard of living and peace of mind."
Figures from the Office for National Statistics have revealed that 52% of households received more in benefits than they paid in taxes during the 2012/13 tax year.
The ONS also said the average disposable income of retired households has risen 7.9% (or (£1,700) in real terms since 2007/08 to just under £21,520 in 2012/13.