Estimation Guide

Detailed techniques for accurate effort estimation in technical roadmaps.

The Estimation Problem

Humans are notoriously bad at estimation, especially for:

• Novel work (never done before)
• Complex work (many unknowns)
• Long-duration work (> 2 weeks)

This guide provides techniques to improve accuracy.

T-Shirt Sizing Deep Dive

Size Definitions

When to Use Each Size

XS - Trivial

• You've done this exact thing before
• No code review concerns
• Can be done and deployed in one sitting

S - Simple

• Clear implementation path
• Single component affected
• Standard patterns apply

M - Standard

• Normal feature work
• May need some research
• Touches 2-3 files/components

L - Complex

• Multiple components affected
• Integration work required
• Some architectural decisions

XL - Very Complex

• Significant unknowns
• New technology/patterns
• Cross-team coordination
• Should consider breaking down

XXL - Epic-level

• Too large for single story
• Must be decomposed
• Red flag if assigned to single item

Estimation Techniques

1. Reference-Based Estimation

Compare to similar past work:

Previous similar feature: 3 weeks
Complexity adjustment: 1.2x (slightly more complex)
Team familiarity: 0.9x (more familiar now)
Estimate: 3 × 1.2 × 0.9 = 3.2 weeks

2. Task Decomposition

Break down until tasks are < 1 day:

Feature: User Dashboard

Tasks:
├── Design API schema (S: 4h)
├── Implement backend endpoint (M: 8h)
├── Create React components (M: 12h)
├── Write unit tests (S: 4h)
├── Integration tests (S: 4h)
├── Documentation (XS: 2h)
└── Code review + fixes (S: 4h)

Total: 38 hours ≈ 5 days
Add 25% buffer: 6.25 days
Estimate: L (3-5 days) → round up to 1.5 weeks

3. Three-Point Estimation

Estimate optimistic, most likely, and pessimistic:

Optimistic (O): Everything goes perfectly = 3 days
Most Likely (M): Normal development = 5 days
Pessimistic (P): Everything goes wrong = 12 days

PERT Estimate = (O + 4M + P) / 6
             = (3 + 20 + 12) / 6
             = 5.8 days

4. Planning Poker

Team-based estimation:

1. Present story to team
2. Everyone estimates privately
3. Reveal estimates simultaneously
4. Discuss outliers
5. Re-estimate until consensus

Adjustment Factors

Multipliers to Apply

Velocity Adjustments

Theoretical capacity:
  5 engineers × 40 hours = 200 hours/week

Realistic capacity (apply factors):
  - Meetings/admin: 0.8x
  - Context switching: 0.85x
  - Interruptions: 0.9x
  - Learning/research: 0.9x

Effective capacity:
  200 × 0.8 × 0.85 × 0.9 × 0.9 = 110 hours/week

That's 55% of theoretical!

Common Estimation Mistakes

1. The 90% Done Trap

Mistake: "We're 90% done" for weeks. Fix: Track tasks to completion, not percentage.

2. Ignoring Integration

Mistake: Estimate components in isolation. Fix: Add explicit integration tasks and testing.

3. Happy Path Only

Mistake: Estimate assumes no bugs, no blockers. Fix: Always add 20-30% buffer.

4. Scope Creep Blindness

Mistake: Estimate original scope, deliver expanded scope. Fix: Re-estimate when scope changes.

5. Anchoring

Mistake: First estimate biases all subsequent estimates. Fix: Use planning poker, estimate independently first.

6. Planning Fallacy

Mistake: Optimism despite past evidence. Fix: Compare to actual duration of past similar work.

Estimation for Different Phases

Phase 1: MVP

• Estimate in detail (story/task level)
• Add 25% buffer
• Expect 20% scope change

Phase 2: Scale

• Estimate at epic level
• Add 30% buffer
• Expect 30% scope change

Phase 3: Advanced

• Estimate at theme level only
• Add 40% buffer
• Expect 50% scope change

Team Velocity

Calculating Historical Velocity

Sprint 1: 34 points completed
Sprint 2: 28 points completed
Sprint 3: 31 points completed
Sprint 4: 35 points completed

Average velocity: 32 points/sprint
Standard deviation: 2.9 points

Conservative estimate: 29 points/sprint (avg - 1 std dev)

Using Velocity for Planning

Total backlog: 180 points
Conservative velocity: 29 points/sprint
Sprints needed: 180 / 29 = 6.2 sprints

Add buffer (20%): 7.5 sprints
Estimate: 8 sprints (4 months with 2-week sprints)

Estimation Checklist

Before finalizing estimates, verify:

• [ ] Broke down items to < 1 week
• [ ] Considered integration time
• [ ] Accounted for testing
• [ ] Included documentation
• [ ] Added code review time
• [ ] Applied technology multipliers
• [ ] Compared to past similar work
• [ ] Added 20-30% buffer
• [ ] Team agreed on estimates
• [ ] Identified dependencies