Charities should be told to say in their annual reports how much tax they reclaim on donations, a Gift Aid consultant will propose to the Charity Commission and the Institute of Fundraising.
Barry Gower, director of the consultancy Gain, said that charities should have to show what proportion of the available benefit had been claimed. Charities had a duty to donors to maximise their income through Gift Aid and other tax-efficient methods, he said, and should be asked to account for whether they were doing so.
Gower will write to the institute and the commission, asking them to recommend his suggestion to fundraising charities.
"Donors should be able to find out whether tax is being reclaimed on the money they are giving to charity - and if it isn't, they should be able to find out why not," he said.
He said charities should already be producing Gift Aid figures internally.
"It's very easy to do, because Gift Aid is accounted for separately from donations in all the accounting programs I've seen," he said.
"But I've frequently spoken to charities that have no idea what proportion of the available Gift Aid they can collect.
"My feeling is that if charities were required to report their success in acquiring Gift Aid, it would be a powerful incentive to improve their results."
A spokeswoman for the Charity Commission said there was no requirement to provide such details in accounts.