Individual donations to charity increased by more than £600m in 2017, according to the largest study of giving in the UK.
But although the sum donated rose from £9.7bn in 2016 to £10.3bn last year, a smaller percentage of people gave.
The decline is mainly due to a two-percentage-point decline in the proportion saying they sponsored someone.
However, the average amount given has increased: the median monthly sum given in 2017 was £20, compared with £18 in 2016. The mean average in 2017 was £44, compared with £40 in 2016.
Although this year's overall figure is up, CAF figures dating back to 2005 show there has been little long-term change in the amount given or in giving habits.
The £10.3bn donated represents the first time that total giving has been above £10bn since 2014, but is only equal to the amount given in 2005, CAF’s figures show. The highest amount given in recent years was £11.6bn in 2010.
Cash remained the most popular form of giving, with 55 per cent of people saying they gave to charity by this method in 2017. November and December, which include the Poppy Appeal, Children in Need and Movember, were the peak months for donations.
"This perhaps demonstrates the point that the UK population is good at reactive giving, such as response to appeals and campaigns, but less so at planned giving," the report says.
CAF has found that men have traditionally given more, but the gap is closing, with the mean average male donation £46 in 2017 compared with £42 for females. The figure for women increased sharply from £35 in 2016.
But men are also more than twice as likely as women to say they rarely or never give to charity (25 per cent compared with 12 per cent). Females are also more likely to volunteer (19 per cent against 15 per cent).
For the first time since the survey began, 16 to 24-year-olds said they gave more than 25 to 34-year-olds.
Susan Pinkney, head of research at CAF, said this was explained by 25 to 34-year-olds giving less, probably because their budgets were being squeezed by rent or mortgage payments, rather than by a surge in donations from 16 to 24-year-olds.
Pinkney said she hoped the report would trigger a debate amongst policymakers about how to stimulate giving. "Looking at male giving in more detail might be a good starting point," she added.
Medical research remains the most popular cause, followed by animal welfare, children and young people, hospitals and hospices, and overseas aid and disaster relief.
In 2017, Londoners were more likely than the rest of the country to give to smaller causes and tackling homelessness. People in Northern Ireland were the most likely to have given to religious organisations, people in Wales were the most likely to have given to animal welfare and people in the south west of England were the most likely to have given to conservation, the environment and heritage.
The report says that trust in charities remained stable: 51 per cent agreed that charities were trustworthy, a figure similar to that of last year.
But it describes the decline in the proportion of people giving as a concern. "This ties in with a key policy question about encouraging giving and whether it should target getting those who give to give more or target getting more people to give – or, indeed, a combination of both," it says.
The survey is based on the results of monthly online polls of 1,000 people conducted by YouGov on behalf of CAF.
Sir John Low, chief executive of CAF, said: "We need to be careful if giving becomes concentrated in fewer, larger donations."
Peter Lewis, chief executive of the Institute of Fundraising, said he was pleased to see total giving up and heartened by the increase in the average amount donated.
But he added: "We continue to see a demographic disparity, with men giving less than women, and the slight decrease in sponsorship levels suggests that fewer people gave money in 2018 than the previous year.
"Fundraisers will be thinking about strategies to address this and how they can get more people giving and people giving more."