The 10% Pledge Is a Goldilocks Number

The 10% giving pledge is not a magic number but sits in a 'Goldilocks zone': a further pledge (capping income and giving everything above) would attract almost no one, while a 1% pledge would not change behavior since people in the UK already give about 0.7% and Americans about 2%—so 10%, with its long religious-tithing history, is large enough to matter yet small enough to be widely adoptable.