Optimistic duration, in project management,  is an estimate of the shortest duration of activity that takes into consideration the known variables that can influence performance. It is part of the activity duration estimate which is defined as the process of making estimates of the number of work periods necessary to complete individual activities using  estimated resources.

Since this particular estimate in project management is based on the consideration of all the variables known that can affect the performance, this activity duration is based on the analysis of the best-case scenario for activities. The optimistic duration is designated in formulas as TO.

It is a part of the three-point estimating used to estimate the activity duration and estimate costs. The three-point estimate uses other duration estimates which include the pessimistic and most likely estimates. The three are used to calculate the estimate especially when there is uncertainty with the activity estimates.

The optimistic duration is necessary for calculating the approximate range of time to complete the project. Without it, it will be challenging to create a timeline of the duration of the activities. This, in turn, will affect the entire project management planning.