estimation

Estimation

Process

1. Decompose Exhaustively

Break tasks until each piece is < 8 hours and estimatable with confidence.

Task: "Add user authentication"
  ├─ Database schema (2h)
  ├─ API endpoints (16h) → decompose further
  ├─ Password handling (8h)
  ├─ JWT tokens (19h) → decompose further
  ├─ Middleware (14h) → decompose further
  ├─ Testing (23h) → decompose further
  └─ Integration (22h) → decompose further

Rule: If you can't estimate confidently, decompose further.

2. Identify Unknowns

unknowns:
  technical:  ["Never used bcrypt", "Don't know JWT refresh pattern"]
  domain:     ["Password rules unspecified", "SSO needed later?"]
  external:   ["DBA review has 2-day SLA"]
  resource:   ["Frontend dev availability uncertain"]

Every unknown adds risk. Quantify it.

3. Three-Point Estimate

For each atomic task:

Estimate	Meaning
Optimistic (O)	Everything goes perfectly
Realistic (R)	Normal conditions, typical hiccups
Pessimistic (P)	Murphy's Law applies

"Implement password hashing"
O: 1h  (copy existing pattern)
R: 3h  (read docs, test, handle edge cases)
P: 8h  (version issues, need alternatives)

Rule: If P > 3x R, decompose further.

4. Calculate PERT

Expected = (O + 4*R + P) / 6

Example: (1 + 4*3 + 8) / 6 = 3.5h

5. Apply Risk Buffers

Risk Level	Multiplier	When
Low	1.0-1.2x	Well-understood, clear requirements
Medium	1.2-1.5x	Some unknowns, moderate complexity
High	1.5-2.0x	New tech, unclear requirements
Critical	2.0-3.0x	Multiple unknowns, bleeding-edge

Risk categories:

Category	Multiplier	Triggers
Technical	1.3-2.0x	New lang/framework, complex algorithms, perf requirements
Domain	1.4-2.5x	Unclear requirements, regulatory, stakeholder disagreement
External	1.5-3.0x	Third-party deps, vendor timelines, cross-team
Resource	1.2-2.0x	Availability uncertain, skills gap, access issues

6. Add Integration Buffer

Integration is where 50% of bugs live. Always add 20-30%.

Subtasks total: 40h
Integration buffer (25%): 10h
Final: 50h

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Anti-Patterns

Anti-Pattern	Problem	Fix
"2 Hours"	"I have no idea"	Use three-point + PERT
Secret Padding	Destroys trust	State explicit buffer: "5h + 5h buffer"
Ignoring Integration	Underestimate 30-50%	Always add integration buffer
Forgetting Testing	"Done" != done	Include test time (often 1:1 with dev)
No Confidence Level	False precision	Use ranges: "45h +/- 5h"

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Communication Template

[ESTIMATE] (+/-[UNCERTAINTY]) assuming [ASSUMPTIONS]

Breakdown:
- Component 1: Xh
- Component 2: Yh
- Integration: Zh

Confidence: [High/Medium/Low] (XX%)

Assumptions:
1. [Critical assumption]

Risks:
- [Risk]: [impact] / [mitigation]

Dependencies:
- [External dependency]

Unknowns:
- [Unknown] - [how to resolve]

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Validation Checklist

Before finalizing any estimate:

• Decomposed into atomic units (< 8h each)
• Every subtask has O/R/P estimates
• PERT formula applied
• All unknowns identified
• Risk buffers applied
• Integration buffer added (20-30%)
• Confidence level assigned
• Assumptions stated
• Risks identified with mitigations
• Dependencies noted
• Estimate is a range (+/- X)

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When to Re-Estimate

• Requirements change -- re-decompose affected components
• Unknown resolved -- update with actual findings
• Overrun > 20% -- stop and reassess remaining work
• Dependency changes -- adjust timeline
• Team changes -- different skills = different estimates

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Script

Run the interactive PERT estimation helper:

skills/estimation/scripts/estimate.sh
# or
./scripts/estimate.sh [--output filename]

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References

• references/decomposition-examples.md -- full worked examples
• references/risk-analysis.md -- risk assessment framework
• references/communication-guide.md -- stakeholder communication patterns
• scripts/estimate.sh -- interactive PERT estimation script