Question regarding integrating bonuses and fees for contractors

[Peter Staiano]

Hey everyone, 

With regards to contractors specifically, when setting up work I have read and heard referenced on BP that some people will work in bonuses for work finished early and fees if work goes over schedule. I was wondering how this is incorporated in real life. Is it a percentage or a flat bonus/fee? What have you used in previous projects? Thanks for the help as always. 

Pete