N9-2: Quantifying Debt in Dollar Terms
The PDI methodology applied: putting an exact dollar value on every line of debt.
🎯 What You'll Learn
- ✓ Apply PDI to real codebases
- ✓ Calculate maintenance load
- ✓ Model interest rate curves
- ✓ Build debt inventories
Lesson 1: The PDI Methodology
The Product Debt Index (PDI) = (Cost of Delay × Dependency Graph Depth) / Automated Coverage %. A PDI > 100 means systemic collapse risk. But PDI must be translated into dollars: multiply the PDI score by the average monthly cost of a blocked feature to get the dollar-equivalent exposure.
Monthly revenue lost because a feature is blocked by debt.
Number of systems that must change for a single feature.
PDI Score × Average Feature CoD = Dollar exposure per debt item.
Run the PDI calculator on your 5 highest-debt components. Convert each PDI score to a dollar value.
Lesson 2: Maintenance Load Analysis
Maintenance Load = percentage of total engineering capacity consumed by non-value-adding work (bug fixes, legacy workarounds, manual deployments). If Maintenance Load exceeds 40%, the team is spending more time fighting the system than building value. This is the "Innovation Tax."
Maintenance hours / Total engineering hours × 100.
Count story points spent on maintenance vs new features per sprint.
If maintenance load grows 2% per quarter, velocity halves in 18 months.
Audit the last 6 sprints and calculate your Innovation Tax trend line. At the current rate, when does maintenance exceed 40%?
Lesson 3: Debt Inventory Construction
A debt inventory is a living document that catalogs every known debt item with: description, estimated remediation cost, annual carrying cost, PDI score, risk level, and owner. Without an inventory, debt is invisible — and invisible debt grows exponentially.
A shared, version-controlled document listing all known debt.
Engineering weeks required to fully resolve each item.
Carrying cost / Remediation cost = bang-for-buck ratio.
Create a debt inventory for your top 10 technical debt items with remediation cost, carrying cost, and priority scores.
Continue Learning: Track 9 — Technical Debt as Financial Liability
2 more lessons with actionable playbooks, executive dashboards, and engineering architecture.
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Module Syllabus
Lesson 1: Lesson 1: The PDI Methodology
The Product Debt Index (PDI) = (Cost of Delay × Dependency Graph Depth) / Automated Coverage %. A PDI > 100 means systemic collapse risk. But PDI must be translated into dollars: multiply the PDI score by the average monthly cost of a blocked feature to get the dollar-equivalent exposure.
Lesson 2: Lesson 2: Maintenance Load Analysis
Maintenance Load = percentage of total engineering capacity consumed by non-value-adding work (bug fixes, legacy workarounds, manual deployments). If Maintenance Load exceeds 40%, the team is spending more time fighting the system than building value. This is the "Innovation Tax."
Lesson 3: Lesson 3: Debt Inventory Construction
A debt inventory is a living document that catalogs every known debt item with: description, estimated remediation cost, annual carrying cost, PDI score, risk level, and owner. Without an inventory, debt is invisible — and invisible debt grows exponentially.