The total surplus made by charities in England and Wales fell by 60 per cent between 2007 and 2009, figures from the Charities Aid Foundation show.
An analysis of annual returns from charities showed that the sector's total surplus, calculated by subtracting total expenditure from total income, fell from £3.59bn in 2007 to £1.45bn in 2009, allowing for inflation.
Total income for charities in England and Wales went up from just less than £51.9bn in 2007 to £55.5bn in 2009, whereas expenditure increased from £48.3bn to £54bn.
The average surplus per charity was £24,507 in 2007, but fell to £10,240 in 2009, the figures show.
Provisional data for 2010 reveals that the overall charity sector surplus increased slightly to £1.51bn.
Colin Walton, head of charities at the Charities Aid Foundation, said: "Our analysis shows just how difficult the past few years have been for charities financially.
"The fall in surpluses makes things extremely difficult for charities because it means less to invest in their organisations and staff, less opportunities to expand their services and less to put aside into reserves.
"Charities have always had to work efficiently, but the situation over the past two to three years has meant more and more charities are working on a financial knife-edge."