How much money that we pay each year to charities ACTUALLY goes on helping people?

Some charities are huge worldwide organisations that employ lots of people. I wonder just how much of our actual donations goes on helping the people they say they support? After directors and management and utility bills have been paid, surely there is very little left that actually goes to help people.. What about charities that work abroad in war zones? They need to have money available to bribe the local militia/army etc..