---
title: "Technical Debt and the Cost of the Next Change"
description: "A shortcut taken today is borrowed time, and the interest is paid by everyone who touches that code afterwards. Some debt is worth taking deliberately; the failure is taking it without recording it or"
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source: https://lightmysky.com/learn/computing/technical-debt-and-the-cost-of-the-next-change-mt_iA8-0Qg4ID.md
retrieved: 2026-09-12
---

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# Technical Debt and the Cost of the Next Change

A shortcut taken today is borrowed time, and the interest is paid by everyone who touches that code afterwards. Some debt is worth taking deliberately; the failure is taking it without recording it or planning when it gets repaid.

Subject: Computing · Area: Software Engineering · Ages 21 to 22
Page: https://lightmysky.com/learn/computing/technical-debt-and-the-cost-of-the-next-change-mt_iA8-0Qg4ID

## Ready when they can

- Identify a shortcut in a codebase and estimate what it costs per change
- Argue for taking on a piece of debt deliberately, with the repayment named
- Distinguish debt from code that is merely old and still fine

## Lesson: Borrowed time and its interest

A shortcut today is borrowed time. Like a loan, it has a principal, the cleanup you skipped, and interest, the extra cost on every later change. Each future change pays part interest and part principal until the debt is gone.

**Example.** You hard-code delivery zones to ship on time. Every new zone now needs a code edit plus testing, which is the interest. The principal is the afternoon needed to move zones into a table.

Some debt is worth taking on purpose, when shipping now matters more than clean code. The deal must name the repayment: what gets cleaned and when. Without a date, interest keeps compounding and nobody repays it.

**Tip.** Old code is not debt if it still reads well and costs nothing extra per change. Call it debt only when you can point at the extra cost each change pays.

**Recap.** Name the shortcut, price its interest per change, schedule the principal, and leave old code that costs nothing alone.

## Practice

14 questions on this page, each with its working shown.

## Needs first

- [Refactoring: Changing Structure Without Changing Behaviour](https://lightmysky.com/learn/computing/refactoring-changing-structure-without-changing-behaviour-mt_HHZufOyTg4)
- [Software Architecture: Layers, Services and Their Trade-offs](https://lightmysky.com/learn/computing/software-architecture-layers-services-and-their-trade-offs-mt_uz_OkFgysJ)

## Opens up

- [Working in a Team: Issues, Estimates and Iterations](https://lightmysky.com/learn/computing/working-in-a-team-issues-estimates-and-iterations-mt_HNNnVvADcF)
- [Scoping and Writing a Thesis-Scale Project](https://lightmysky.com/learn/computing/scoping-and-writing-a-thesis-scale-project-mt_Y46uRENRVf)