When I am making a price estimation in some project, I try to predict the number of work hours based on my experience or my logic. Of course, many times you face features you did not implement before and then you have to guess number of work hours. And in such cases, I am usually wrong and then I have to work extra hours for free since the clients usually say "sorry we do not have any more money in this project for extra costs".
Now, I know that companies usually count these extra work hours into its price. For example, if they estimate that they need 100 man hours, then they multiply 100 with some percentage to get the final estimation. Some other use standard deviation formulas, and so on.
I have 2 questions:
- Can you tell me what percentage do you use to calculate all extra man hours for all unpredicted events?
- Do you increase number of work hours on your own or you make a special time milestone called "Extra hours" or "unpredicted events" which you spend in case you come across event I described here?
NOTE: Since I am not sure which terminology to use, anyone can fix the title to make it better! It's possible that these extra hours in some project have its own name and I do not know it. Thanks!