The institute told an assembly of 100 fundraisers who came to the convention launch in London last week that the range of accommodation available in the capital makes for a more flexible and cheaper deal.
"Running the convention in Birmingham has made a hole in the budget," said Lindsey Boswell, chief executive of the institute.
"Birmingham was a residential conference, and we wanted to separate the learning from accommodation to allow delegates to pay only for what they need. This year's event is 30 per cent cheaper and 30 per cent bigger," he said.
Boswell added that research carried out over the past three years showed that most delegates live in London and the south east.
This year's convention will include debates on broader themes, such as fundraising and public perceptions.
"This is a huge issue that charities cannot expect to get away from," said convention chairman Julius Wolff-Ingham.
With more sessions and speakers over three days, the institute hopes to attract 600 more delegates than the 1,400 who came last year.
- The convention will be held at the Hilton London Metropole from 11-13 July
- The 168 sessions will be delivered by 200 fundraisers, a 30 per cent increase on 2004
- The event has been lengthened from two and a half to three days
- New topics include 'Fundraising and public perception' and 'Fundraising department makeover'.