What percentage of overall project effort do you budget for program management?

Agree with the others in that it depends on the project, and on the maturity of the organization. For smaller, less complex projects, you might be able to get by on 5-10% or less if the organization doesn't require formal tracking/reporting. For medium sized projects 10-15% may be more reasonable, and then for very large/complex projects that could extend up to the 25% point. Best to determine the organizational needs for information and oversight, and then then adjust as necessary.

Depends on program complexity and stage. Between 15-20%

Depends on the complexity of the program - I would generally estimate 10-25%.

I would estimate 10-15%