There are two ways in which you can calculate the three-point estimation:

Triangular Distribution E = (P+M+O)/3
Beta or PERT Distribution
E = (P+4M+O)/6
where P = pessimist, O = Optimist, M = most likely.

The three-point estimating method is a technique used in project management to estimate the duration or cost of an activity or project task by considering three different estimates: optimistic (O), pessimistic (P), and most likely (M). The formula for calculating the three-point estimate is typically expressed as:

$E = 6 O + 4 M + P$

Where:

$E$ represents the expected (or average) estimate,
$O$ is the optimistic estimate (the best-case scenario),
$P$ is the pessimistic estimate (the worst-case scenario), and
$M$ is the most likely estimate.

This formula emphasizes a weighted average approach, giving more weight to the most likely estimate while still considering the extremes of optimistic and pessimistic scenarios. This method helps in incorporating a range of possibilities into the estimate and provides a more realistic expectation of the project duration or cost.