Contingent means that an event may or may not occur in the future, depending on the fulfillment of some condition that is uncertain. This term is often used in contracts where the event will not take effect until the specified condition occurs.
This contingency is normally calculated as a percentage. If the phase is 100 days of effort, contingency at 20% would be another 20 days. As the project progresses, the level of risk reduces as the requirements and issues become known, so the percentage will be reduced.
The most basic way to calculate a contingency reserve is to add a fixed percentage to the total project budget, known as the Flat Rate method. Alternatively, if different percentages are applied to unique budget line items, this would be called a Mixed Rate method to establish the reserve.
Home builders and remodelers usually allocate between 5% and 10% of a project budget for a construction contingency. This amount creates enough breathing room for unexpected costs. Anyone tracking estimates and costs manually will calculate a contingency percentage on top of all costs before profit margins are applied.