If that 20% isn't for project management, then add another 10-20% for that, based on experience from previous projects for the same stakeholders. My similar rul

If that 20% isn't for project management, then add another 10-20% for that, based on experience from previous projects for the same stakeholders. My similar rule of thumb is to multiply my estimate by 2.5, before adding the project management percentage. Of course, if it's something we've done before, it's more along the lines of 1.5 to 2.