Pert Estimate

PERT estimate is also called three-point estimation and used to calculate time and costs. It extends the two-time method by adding weight to the estimation of best-case, likley-case and worst-case.

More common is the "Weighted 3-point estimate":

Best Case + 4 x Likely Case + Worst Case
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With this you get a weighted likely case. But when using this calculation it is very important the project manager updates this assumptions frequently.