Three-Point Estimation (PERT)

Confidence Intervals:

• 68% confidence: Estimate ± 1 SD
• 95% confidence: Estimate ± 2 SD
• 99.7% confidence: Estimate ± 3 SD

Benefits

More Realistic Estimates

• Accounts for uncertainty
• Balances optimism and pessimism
• Based on range rather than single point
• Reflects real-world variability

Risk Assessment

• Standard deviation shows uncertainty level
• Identifies high-risk tasks
• Supports contingency planning
• Improves decision-making

Better Than Single-Point

• Single estimates tend toward optimism
• Doesn't account for unknowns
• Three-point captures range of outcomes
• More defendable to stakeholders

How to Apply

Step 1: Break Down Work

• Divide project into tasks
• Make tasks estimable (not too large)
• Identify dependencies

Step 2: Gather Team Input

• Involve people who'll do the work
• Discuss assumptions
• Consider historical data
• Account for known risks

Step 3: Create Three Estimates

For each task:

1. Optimistic: What if everything goes right?
2. Most Likely: What's our realistic estimate?
3. Pessimistic: What if we hit obstacles?

Step 4: Calculate

• Apply formula (usually PERT: (O+4M+P)/6)
• Calculate standard deviation
• Sum estimates for total project time
• Add buffer based on uncertainty

Step 5: Review and Refine

• Sanity check results
• Compare to historical projects
• Adjust for unique factors
• Get team buy-in

Common Mistakes

Too Optimistic Across Board

• All three estimates are optimistic
• Doesn't truly represent worst case
• Solution: Challenge assumptions

Pessimistic = Catastrophic

• Worst case includes disasters
• Not realistic for planning
• Solution: Pessimistic should be bad but plausible

Anchor Bias

• First estimate influences others
• All three cluster too closely
• Solution: Estimate independently or use ranges

Forgetting Dependencies

• Estimates assume parallel work
• Ignore sequential constraints
• Solution: Consider critical path

Use in Agile

Story Point Estimation

Can use three-point for complexity:

• Optimistic: 3 points
• Most Likely: 5 points
• Pessimistic: 8 points
• Weighted estimate: ~5 points

Sprint Planning

• Estimate capacity with three scenarios
• Plan for most likely
• Understand risk with pessimistic

Release Planning

• Project completion dates
• Account for velocity variance
• Communicate uncertainty to stakeholders

Tools and Techniques

Planning Poker Variant

1. Team estimates optimistic
2. Team estimates most likely
3. Team estimates pessimistic
4. Calculate using PERT formula

Monte Carlo Simulation

• Run thousands of simulations
• Use three-point estimates as inputs
• Generate probability distributions
• More sophisticated analysis

When to Use

Good For:

• Complex, uncertain projects
• High-stakes deliverables
• Projects with significant unknowns
• First-time initiatives
• Communicating risk to stakeholders

Less Useful For:

• Routine, well-understood tasks
• Very short tasks (overhead not worth it)
• When single estimate is accurate enough

Ideal For

• Project managers
• Agile teams doing estimation
• Anyone planning complex work
• Organizations needing realistic timelines
• Teams learning to estimate better