Rapp's survey of 1,000 UK adults over 25 also found that another 8% said they were considering cancelling and another 11% were considering lowering the amount they donate.
Rapp planning director Gavin Hilton is advising charities to keep communicating with people who have cancelled their donations. He suggests that they could be offered options such as payment holidays, a one-off donation or other ways to stay engaged with the charity without a financial contribution.
The survey also asked respondents whether they were supporting charities in different ways than a year ago, and 47% said they had started donating clothes or goods.
Hilton said: "Charities should embrace the philosophy that getting close to your customers/donors is always important but never more so than in an economic downturn.
"There will need to be a greater focus on anti-attrition measures, reinforcing the importance of donor support and what their money is achieving, as well as thanking donors.
"Ultimately, strategies may have to move towards more promotion of cash giving as people generally become less confident about making longer term commitment."
Rapp works for a range of charities including the NSPCC and Crisis.