Fewer than two-thirds of charities allow supporters to set up direct debits on their websites, according to research by payment processing firm Rapidata.
The research, based on a survey of 90 charities in June, showed that 63 per cent of their websites included a function for setting up direct debits online.
Seventy-five per cent of charities with annual voluntary incomes of £1m or more allowed users to set up direct debits online, but only 43 per cent of smaller charities did so.
More than 90 per cent of the charities surveyed said they allowed at least one form of online giving. Eighty-three per cent said they accepted credit card donations, and 86 per cent allowed online givers to use Gift Aid. Eighty-nine per cent used email to fundraise, and 79 per cent used social media.
Scott Gray, managing director of Rapidata, said: "Charities have been quick to adapt to new fundraising techniques, but they are missing a trick when it comes to facilitating regular giving online.
"Almost eight out of 10 charities use social media to raise funds, so it's surprising that relatively few are using online direct debits."