ACEVO has published a guide to help charities calculate their core costs and present the true cost of running services to funders.
Funding our Future II: Understand and Allocate Core Costs is a step-by-step guide written by Martin Brookes of the charity New Philanthropy Capital.
ACEVO's chief executive Stephen Bubb said: "This is a seminal piece of work. All third-sector organisations should use it to analyse, review and allocate costs. We then expect the Government and others to fully fund the costs of all projects and contracts," he said.
ACEVO is to work with NCVO to ensure that the manual is incorporated into the Compact code of good practice on funding.
The Charity Commission has also backed the guide.
Chief commissioner John Stoker said: "The manual will help organisations to explain, understand and even compare their costs."