People are being urged to leave a gift to charity in their will as a way of boosting their funds.
Co-op Legal Services said charities were missing out on donations from millions of adults, as only one in 16 have left a gift.
The Co-op asks all its clients writing a will if they want to leave a gift to charity, raising an estimated £20 million.
Poverty, cancer, animal and children's charities top the list of those being left something by a Co-op client.
James Antoniou, head of wills for Co-op Legal Services, said: "We work with a number of large and smaller charities offering affordable will writing services to their supporters.
"As such we understand that there is certainly a desire for clients to leave charitable gifts in wills and this is something that the charities heavily rely on."