Technical Debt in SaaS Companies

Most writing about technical debt treats it as an internal engineering concern — messy code, the kind of thing a team should clean up between releases. For a SaaS company that framing badly understates the stakes, because in a software business the codebase is not a supporting system that helps you deliver the product. It is the product. The thing customers pay for, the thing an acquirer buys, the asset on which the whole company’s value rests, is the same code carrying the debt.

That single fact changes everything about how debt should be understood. A bank’s core ledger can carry decades of cruft and the bank still sells loans; the legacy system is a cost center. In a SaaS company the legacy system is the revenue line. So debt does not just make engineering’s life harder — it slows the roadmap you sell, discounts the valuation you raise against, and quietly grows the bill for keeping the lights on. This series is about modernizing that codebase without stopping the thing that pays for it. This first part is about seeing the problem clearly.

The codebase is the product

Start from the consequence, because it reframes the whole conversation. When the product and the legacy system are the same artifact, you cannot quarantine the debt. You cannot run the old system in a corner while the business moves on, the way an enterprise sometimes can with a back-office mainframe. Every feature you ship, every customer you onboard, every integration you sell runs through the code that carries the debt — so the debt sits in the critical path of growth, not off to the side of it.

This is also why “we’ll deal with it later” is more dangerous in SaaS than almost anywhere else. Later, the code will have more customers depending on its exact current behavior, more features built on top of the workarounds, and fewer of the original engineers still around to explain why any of it works the way it does. The debt does not wait politely. It sets in.

Three places the debt shows up

Technical debt in a SaaS company surfaces in three distinct, measurable places — and naming them is the first step to making the case to anyone outside engineering.

The roadmap slows down. This is the symptom engineers feel first and executives notice eventually. Features that would have taken a week take a month, not because the team got worse but because each change now has to navigate the accumulated workarounds, the brittle couplings, the test suite nobody trusts. Stripe’s 2018 study The Developer Coefficient put the time developers lose to technical debt and bad code at roughly 42% of their time — close to half of paid engineering capacity spent fighting the codebase rather than extending it. In a SaaS company, that lost capacity is roadmap that never ships, against competitors who may be carrying less of it.

The valuation takes a discount. The moment a SaaS company raises a serious round or entertains an acquisition, a buyer’s technical due diligence reads the actual code — architecture, dependency health, security posture, how much critical knowledge sits in how few heads. Debt that was invisible on the income statement becomes a line of concrete findings, and every finding is grounds for a lower price, an earnout, or an indemnity. Technology risk moving a deal price is not hypothetical; the widely cited case is Verizon’s reduction of its Yahoo acquisition price after an undisclosed breach. The code you have been deferring work on is the asset someone else is about to appraise.

The budget tilts toward standing still. As the product ages, a larger share of engineering goes to keeping it running rather than moving it forward — bug-fixing, firefighting, dependency upgrades, the work that produces no new value but cannot be skipped. Deloitte’s Global CIO surveys put run-the-business spend at roughly 55–57% of the IT budget across organizations generally; a debt-heavy product pushes a SaaS company’s own ratio higher. McKinsey’s October 2020 analysis framed the same drain from the asset side, estimating technical debt at 20–40% of an entire technology estate’s value. The money is real, and it is being spent on yesterday’s product.

Why it compounds

The reason debt is dangerous rather than merely annoying is that it compounds, and the mechanism is worth being precise about. Each shortcut or aging decision makes the code around it harder to change. So the next feature gets built on top of the workaround rather than on a clean foundation — adding a second workaround, which the third feature then builds on. The structure tangles. Meanwhile two clocks run in the background: the engineers who understood the early decisions leave and take the context with them, and the dependencies the product was built on march toward end-of-life. The interest rate on the debt climbs even in a quarter where you ship nothing new. That is why a codebase that felt fast and clean at launch can feel close to unworkable a few years later without any single bad decision you can point to. The full mechanics of compounding debt are the subject of our technical-debt series; here the point is simply that doing nothing is not holding steady. It is falling behind on a curve.

The tension that defines the problem

Here is what makes SaaS modernization genuinely hard, and why the rest of this series exists. You cannot stop shipping to fix it. An enterprise modernizing a back-office system can sometimes freeze it, migrate, and cut over. A SaaS company cannot freeze its product — the roadmap is how it competes, retains customers, and justifies its valuation. The customers keep needing new features; the market keeps moving; the board keeps expecting growth. So the work has to happen on a moving target: modernize the product while it is live, serving customers, and shipping.

That constraint rules out the instinctive answer, the big rewrite, more firmly in SaaS than anywhere. A multi-quarter rewrite is a roadmap freeze by another name, and the failure rate is sobering — BCG found in September 2023 that up to 70% of digital transformations fail to deliver on their objectives. The realistic path is the opposite of a freeze: modernize the product slice by slice, proving each slice behaves identically to the old one before it carries live traffic, so the roadmap never stops and the risk stays bounded. That is the approach this series builds toward, and the approach behind ModernLift’s work.

Knowing which debt to leave alone

Not all debt is worth paying down, and a series that pretended otherwise would be easy to dismiss. Debt in a stable part of the product that nobody touches, that runs fine and faces no end-of-life pressure, may be cheaper to leave than to fix. The debt that matters is the debt in the path of where the business is trying to go — the modules the roadmap keeps colliding with, the architecture that throttles scale, the dependencies sliding out of support. Part of the discipline this series teaches is telling the difference, so you spend modernization effort where it returns roadmap and valuation rather than spreading it evenly out of tidiness.

Where this leads

We have established the frame: in a SaaS company the codebase is the product, debt taxes the roadmap and the valuation and the budget, it compounds, and you cannot stop shipping to fix it. The natural next question is how to tell when the problem has grown past ordinary debt into something structural — when it is not the code that has aged but the architecture the product has outgrown. Part 2, When Your SaaS Outgrows Its Architecture, lays out the symptoms that distinguish a codebase that needs cleanup from one that has hit a structural ceiling.