nixos-config/profiles/opencode/skill/spec-planner/references/estimation.md

Estimation

Why Estimates Fail

Cause	Mitigation
Optimism bias	Use historical data, not gut
Missing scope	List "obvious" tasks explicitly
Integration blindness	Add 20-30% for glue code
Unknown unknowns	Add buffer based on novelty
Interruptions	Assume 60% focused time

Estimation Techniques

Three-Point Estimation

Expected = (Optimistic + 4xMostLikely + Pessimistic) / 6

Relative Sizing

Compare to known references:

• "This is about twice as complex as Feature X"
• Use Fibonacci (1, 2, 3, 5, 8, 13) to reflect uncertainty

Task Decomposition

1. Break into tasks <=4 hours
2. If can't decompose, spike first
3. Sum tasks + 20% integration buffer

Effort Multipliers

Factor	Multiplier
New technology	1.5-2x
Unclear requirements	1.3-1.5x
External dependencies (waiting on others)	1.2-1.5x
Legacy/undocumented code	1.3-2x
Production deployment	1.2x
First time doing X	2-3x
Context switching (other priorities)	1.3x
Yak shaving risk (unknown unknowns)	1.5x

Hidden Work Checklist

Always include time for:

• Code review (20% of dev time)
• Testing (30-50% of dev time)
• Documentation (10% of dev time)
• Deployment/config (varies)
• Bug fixes from testing (20% buffer)
• Interruptions / competing priorities

When to Re-Estimate

Re-estimate when:

• Scope changes materially
• Major unknown becomes known
• Actual progress diverges >30% from estimate

Communicating Estimates

Good: "1-2 weeks, confidence 70%-main risk is the third-party API integration"

Bad: "About 2 weeks"

Always include:

1. Range, not point estimate
2. Confidence level
3. Key assumptions/risks