The organisation is now advising clients giving a total of £1m a month - three times the figure recorded at the end of 2005.
It attributes the increase largely to improved reporting about how money is spent by the health, education, family and community charities it recommends to the rich.
Harry Charlton, head of client development at NPC, said: "One of our key performance indicators is the amount of money we advise on that flows from donors to our charities.
"We ask our clients how they feel about giving, and they find it comforting to know that their money is put to good use and that it can be demonstrated objectively. This has led to an increase in demand for our services."
Susan Mackenzie, director of research organisation Philanthropy UK, said that anecdotal evidence suggested giving was increasing, but only among the wealthiest.
"The richer rich - those that appear on the Sunday Times Rich List, for example - are certainly giving more," she said. "But that doesn't mean all high net-worth individuals are doing so. There is much more still to be done."