estimation

<!-- Last reviewed: 2026-03 --> # 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 ```yaml 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 ``` --- ## 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" | --- ## 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] ``` --- ## 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) --- ## 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 --- ## Script Run the interactive PERT estimation helper: ```bash skills/estimation/scripts/estimate.sh # or ./scripts/estimate.sh [--output filename] ``` --- ## 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