When to build custom software instead of buying

The default answer should usually be: buy first

Custom software is powerful, but it is not automatically better. Thoughtworks frames the tradeoff clearly: buying provides proven capabilities faster but with less customization and control, while building gives the organization a closer fit at greater expense and effort. Mature SaaS products have already absorbed years of product design, security work, edge cases, maintenance, support, integrations, and user feedback. Rebuilding a commodity function from scratch rarely creates an advantage.

If the company needs payroll, accounting, email marketing, standard CRM functionality, project management, or another common business system, the right product often already exists.

The problem begins when the business is not actually using the software as intended because the underlying workflow is different from what the product assumes.

Signal 1: the team has built a shadow system around the software

Spreadsheets, shared documents, email threads, copy-and-paste routines, manual exports, browser tabs, and “make sure you also update this sheet” are clues that the purchased system is only part of the real workflow.

One workaround is normal. A web of workarounds is different. At that point the company is effectively maintaining custom software already—it is just doing it manually, with humans acting as the integration layer.

The useful question is not whether a workaround exists. It is how much time, risk, delay, and inconsistency the workaround creates every week.

Signal 2: the workflow is part of how the company competes

Some processes are generic. Others are part of the company’s advantage. A specialized lead-routing system, quoting workflow, production planner, compliance process, client portal, field-reporting tool, or internal decision engine may encode knowledge that differentiates the business.

If the software forces that process to become generic, the company may be giving up an advantage in exchange for convenience.

Custom software is most defensible when it supports a process the company understands deeply and intends to keep refining.

Signal 3: integration cost has become the real subscription price

A SaaS product may appear inexpensive until the surrounding costs are included: duplicate entry, middleware subscriptions, custom connectors, consultant hours, data cleanup, reconciliation, and staff time spent moving information between systems.

This is why purchase-versus-build comparisons should use total operating cost. The UK Government Service Manual makes the same point in its technology-selection guidance: teams should minimize total cost of ownership, reduce avoidable vendor lock-in, retain control of their data, and make choices that can adapt as user needs change. A $300 monthly tool that triggers substantial manual work may be more expensive than the subscription suggests.

Conversely, a custom system that requires continual engineering attention can be far more expensive than expected. Both sides of the comparison need to include maintenance, support, security, upgrades, hosting, and organizational change.

Signal 4: the company needs control over data, logic, or user experience

Ownership matters when the business needs to control how data is structured, how rules are applied, how systems interact, or how customers and employees experience a workflow.

A custom application can be designed around the exact data model and business rules rather than exposing only the options a vendor chooses to support.

That flexibility has value, but it also creates responsibility. The company—or its development partner—now owns reliability, security, backups, access control, documentation, and ongoing product decisions.

A practical build-versus-buy framework

Define the business outcome

Describe the result the workflow needs to create before comparing products or technologies.

Map the current process

Document the real process, including spreadsheets, approvals, handoffs, integrations, exceptions, and rework.

Estimate the cost of friction

Measure staff time, delays, errors, lost opportunities, duplicate tools, and operational risk.

Test existing products honestly

Evaluate whether configuration, APIs, automation, or a different SaaS product can solve the problem without a full custom build.

Identify the differentiating logic

Separate commodity functionality from the process that is genuinely unique to the business.

Model three-year ownership

Compare subscriptions and implementation against development, hosting, maintenance, support, upgrades, and internal change management.

Start with the smallest valuable version

If custom wins, build the narrowest workflow that proves the business value before expanding.

Hybrid is often the best answer

The decision does not have to be all SaaS or all custom. Many of the strongest systems use proven products for commodity functions and custom software for the differentiated layer. Digital.gov’s modernization guidance makes a related point: user research should happen before the build-versus-buy decision so teams can compare actual needs and pain points against what the market already provides instead of choosing a technology path first.

A company might keep its accounting platform, email service, CRM, and identity provider, then build a focused internal application that coordinates the unique workflow across them through APIs.

That approach avoids rebuilding mature infrastructure while still giving the business control where control creates value.

Questions that usually reveal the answer

Would we change our process to fit the software if there were no switching cost?

If yes, the process may not be strategically unique enough to justify a build.

Are employees doing repetitive work because systems do not talk to each other?

If yes, integration or automation may solve the problem before a full application is necessary.

Does this workflow directly affect revenue, margin, speed, quality, or customer experience?

The closer the workflow is to business value, the easier it is to justify deeper investment.

Can we explain what success looks like in measurable terms?

If not, the software project is probably not scoped tightly enough yet.

Who will own the product after launch?

If there is no clear answer, custom software can become an orphaned system.