Tech Debt Interest
Initial fix × (1 + growth)^months — velocity makes the exponent larger.
Payoff hours = initial fix × (1 + growth × (1 + velocity/10))^months. Features built on top compound the drag.
Tech debt isn't a vibe — it's a compounding cost function. Every new feature built on top of a hack makes the payoff larger. Quantifying it forces the conversation about when, not whether, to pay it down.
Part of: Saving & Spending Calculators
Quick answer
Payoff hours = initial fix × (1 + growth × (1 + velocity/10))^months. Features built on top compound the drag.
Key points
- ▸ Payoff grows exponentially: 8%/mo compounds to ~3× in 18 months, ~6× in 24.
- ▸ Code velocity multiplies growth: if 5 features land on the hack per month, effective growth rate is ~1.5× the base.
- ▸ Heatmap bands: <10hr green (manageable), 10–25hr warn, 25–60hr amber, 60+ red (must pay down before more builds on it).
- ▸ Not all debt compounds — isolated shortcuts in dead code decay slowly. Touch-frequency is the key signal.
- ▸ The best time to refactor is before the next feature lands on top.
Examples
- Typical hack6hr shortcut, 8%/mo growth, velocity 5 → 4×payoff at month 12. Schedule repayment by month 9.
- High-churn module6hr shortcut, 12%/mo growth, velocity 8 → 10× payoff at month 15. Don't ship without a plan.
- Low-churn utility6hr shortcut, 2%/mo growth, velocity 1 → 1.3× payoff at month 12. Can wait if priorities are elsewhere.
When to use which tool
- Tech Debt InterestMain tool — compound projection with heatmap.Quantify the compounding hours to fix a shortcut as the codebase grows on top of it. Maintenance heatmap.
- Hire vs AutomateFor deciding if a refactor or replacement tool is cheaper than ongoing maintenance.Should you hire a human at $X/hr or pay $Y/mo for a SaaS/automation stack? Efficiency bar comparison.
- Revenue per HeadEngineering velocity is an input to the whole RPH question.Estimate whether the next hire raises or lowers revenue per employee after management time and ramp-up.
Related
- Tech Debt InterestQuantify the compounding hours to fix a shortcut as the codebase grows on top of it. Maintenance heatmap.
- Hire vs AutomateShould you hire a human at $X/hr or pay $Y/mo for a SaaS/automation stack? Efficiency bar comparison.
- Revenue per HeadEstimate whether the next hire raises or lowers revenue per employee after management time and ramp-up.
- The CrossoverThe exact month when a monthly subscription overtakes a one-time lifetime purchase. Opportunity-cost toggle included.
Frequently asked questions
› What growth rate should I use?
5–10%/mo for actively-developed modules; 15%+ for hot paths with constant feature additions; near 0 for stable utilities.
› Is this quantitative or just directional? Trust & accuracy
Directional — an order-of-magnitude tool. The point is to force scheduling, not to nail the hour count.
› How should I use this guide with a Kefiw tool? How-to
Use the guide as the plan and the linked Kefiw tool as the check. Read the steps first, try the move manually, then use the tool to compare outputs, catch edge cases, and decide whether the result actually fits your task.
› What mistake do tool guides help avoid? Troubleshooting
Tool guides help avoid using a utility mechanically without understanding what you are trying to accomplish. Most word, writing, and text utilities are fast, but speed can hide context mistakes. Know whether you are solving a puzzle, cleaning copy, drafting a line, or checking a rule.
› Can a tool guide help me learn the skill? How-to
A tool guide can help you learn if you pause before accepting the output and ask why it worked. Compare your first guess with the tool result, look for the rule or pattern, and repeat that review. Passive copying solves one task; active review builds the skill.