In a study for Age UK, 11% described themselves as finding it difficult or "really struggling" to cope.
The face-to-face survey of 1,258 people suggested 19% cut back on heating this winter in order to manage their money.
Age UK is launching a campaign for over-60s to claim all the benefits they are entitled to receive.
The research found some 26% pensioners said they were buying cheaper or less food and 19% going out less.
Among poorer pensioners, the figures rose to more than a third, or 35%, buying cheaper or less food, and 21% going out less.
A total of 11% said they were in debt through mortgage, credit cards or bank loans.Missed benefits
The findings were released to coincide with Age UK's More Money in Your Pocket campaign, which says as much as £5.4bn in pensioner benefits goes unclaimed each year.
The charity says this is often because people are unaware of the help available.
It says just under a half of pensioners are entitled to pension credit but a third of people eligible do not claim, while up to 1.97 million pensioners are also missing out on council tax benefit worth £1.5bn a year.
Michelle Mitchell, Age UK charity director, said: "At a time when so many people are struggling financially, it is unacceptable that vital benefits are failing to reach some of the poorest and most vulnerable older people in our society.
"This is money that could make a huge difference to people's quality of life. Ultimately, the best way to ensure that people receive the benefits they are entitled to is for them to be paid automatically.
"But in the meantime, the evidence shows that clear, independent information and advice and face-to-face communication are key to improving the take-up of benefits."
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