The report, published today, suggests charities should prompt donors who give through payroll giving or direct debits to increase the value of these donations.
"Charities should begin conversations with supporters to explain that their regular donation might not be worth as much as it was when they first began to help," it says.
It points out that a £10 donation made in 2000 was worth £8.46 in real terms in 2008.
Liz Goodey, head of research at CAF, said: "Charities need to be aware of the effects inflation has both on their costs, which increase, and on the value of their donations - which, if they remain static over time, decrease.
"Although all fundraising charities are affected, the larger charities, which have high outgoings and many regular donors using direct debit and payroll giving, are most badly affected."