Owner caused delay - most basic cost %?

Ok, so there is an owner caused delay, say it is 30 days.  So the Contractor gets a 30 day time extension and what % of Gen. OH costs = 4%, 6% of contract value - what is the general rule of thumb?  I know there are 10 ways to calc it, what is most simple?  what is most common?  If there was a cost loaded schedule, couldn't they supercede that simply because accounting has better numbers or industry precedence?