An estimate is a probability range, not a commitment.
Give three numbers per category, not one. PERT computes expected value (μ) and uncertainty (σ). Commitment is a separate decision on top of this.
PERT formulas
Per estimated item (category), from optimistic O, nominal N, pessimistic P:
$$\mu = \frac{O + 4N + P}{6} \qquad \sigma = \frac{P - O}{6}$$Combined across all items (expected values add; variances add, not σ):
$$\mu_{\text{total}} = \sum_i \mu_i \qquad \sigma_{\text{total}} = \sqrt{\sum_i \sigma_i^{\,2}}$$Confidence bands: \( \mu \pm \sigma \) (~68%), \( \mu \pm 2\sigma \) (~95%). Newness multiplies each nominal \(N\). This communicates uncertainty; it is not a guarantee.
View:
Expected (μ): 0 h σ = 0 h
~68% confidence: 0 h | ~95% confidence: 0 h
Note: