>Then finally you can say with a straight face that 20% of estimated time is for unforseen circumstances. This is how I always have done it across multiple job

>Then finally you can say with a straight face that 20% of estimated time is for unforseen circumstances. This is how I always have done it across multiple jobs and I always called that extra contingency. Depending on the project I sometimes had to ask for over 50% of the total as contingency. If anyone queried it I would explain that it is very likely we'll need it based on my experience of many other projects. Then the client would either accept it as is, or they would want to split the proposal into "what we will definitely pay for" and "what we will pay for only when it is actually needed" which is also fine for both sides if proper progress reporting has been agreed in advance. Someone could think that no client would agree to such a contract as it would open them to be taken advantage of by an unscrupulous supplier, but at the end of the day what matters in business is trust. If a client doesn't trust the supplier they shouldn't hire them. And in all my previous projects I never met an engineer or developer that would deliberately use up the contingency time when it is not needed as everyone knows the availability of this extra time might come very important towards the end of the project.