Retired Britons need to find an extra £2,600 on top of their state pension even if they get the maximum amount.
State pension payments are set to increase 8.5 percent next April, with the full new state pension increasing to £221.20 a week, or £11,502 a year.
But the amount a single person needs for a basic retirement is set to be £14,143 next year, according to calculations by interactive investor, leaving a £2,641 shortfall.
Alice Guy, head of Pensions and Savings at the group, warned many pensioners face an even bigger shortfall.
She said: “Millions of older pensioners receive much less than the headline state pension figures as the higher ‘new state pension’ was only introduced in 2016.
“Older pensioners who retired before April 2016 are only due to receive £8,816 next April – their income will fall an enormous £5,330 short of the amount needed for a basic income in retirement.
“It’s important for those still working to save into a workplace or private pension to supplement the state pension as the state pension alone won’t be enough for a comfortable retirement.”
The group based its figures on the Retirement Living Standards figures from the Pensions and Lifetime Savings Association, which it adjusted for inflation to give a figure for next year.
Under the current figures, a single person needs £12,800 a year for a basic standard of living in retirement while a couple need £19,900.
This provides enough for £54 a week on food and a week and a long weekend of holidays each year.
A single person wanting a comfortable retirement currently needs £37,300 a year while a couple need £54,500 a year.
Asked what state pensioners with a shortfall can do to increase their income, Ms Guy told Express.co.uk: “If you’re short of money in retirement then it’s important to make sure you’re claiming everything you’re entitled to.
“It’s estimated that around 800,000 households are missing out on pension credit, which works by topping up your income to £201.05 if you’re single and £306.85 if you’re with a partner.
“It will also open the door to a range of other benefits like housing benefit and free prescriptions.
“If you’re struggling financially then it’s important to speak to someone for help. Charities like Stepchange specialise in helping people who are in debt or managing on a tight budget and have trained advisors who may be able to help you maximise your income.”
For the latest personal finance news, follow us on Twitter at @ExpressMoney_.
