Nearly half of women aged 40 and over who are living with a partner have no pension of their own, research from Prudential has found.
The survey suggested that many couples in the UK are "sleep-walking into retirement poverty" as they have no idea how much cash they will need to live on.
Prudential found that 46% of women aged 40-plus who lived with a partner face relying on their other half's pension as they did not have one of their own.
Vince Smith-Hughes, head of business development at Prudential, said: "Women who think they can rely on their other half's pension income without having discussed retirement plans with their partner - and preferably with a financial adviser too - could find themselves in financial trouble, especially if they outlive their loved one.
"Sitting down together and working out jointly what you will need to live on is an important part of making the right provision for the future.
"People may feel they can't afford to significantly boost their retirement savings in the current financial climate, but taking even the smallest of steps can have a positive impact.
"Joining a workplace pension scheme, considering a joint life annuity, so the income will continue after one partner dies, and topping up National Insurance contributions are all options which can increase income in retirement."
A Department for Work and Pensions spokeswoman said: "We know people are not saving enough to have the lifestyle they want in retirement.
"That's why reforming the system is so crucial - we want to make it simpler so people understand how much they need to save, and fairer so women are not penalised for taking time off to care for their families.
"Automatic enrolment will also mean that millions of people will start saving with a contribution from their employer, many for the first time."