Britons have an average of £20.55 stashed around their homes in loose change, a charity said.
People are most likely to find money in bedrooms, sofas and clothing, research by the MicroLoan Foundation found.
The poll of 3,000 people showed 83% spent the change on themselves - usually on chocolate, takeaways and cigarettes.
The charity, which provides small loans, business education and mentoring support to impoverished women in sub-Saharan Africa, has launched a Pennies for Life campaign.
It is asking people do donate pennies each time they update their status on the Facebook and Twitter websites.