Build vs Buy Calculator — Custom Software vs SaaS, Scored in 60 Seconds

Five years ago this decision had a default answer. Buy. SaaS was cheaper than building, deployment was simpler, vendor maturity was higher than most in-house engineering organizations. The default has shifted. Per-seat SaaS pricing has compounded at 8-12% annually, customization platforms (Salesforce Apex, HubSpot Operations Hub, Monday.com automations) charge ever more for “configuration” that never quite fits, integration costs balloon as Zapier and Workato and middleware tax every connector, and the maturity gap between modern dev tooling and platform extensibility has narrowed. The result: more teams are quietly running custom builds where they used to settle for SaaS. The hard part is deciding which side of that line your specific situation falls on.

This calculator scores six factors that reliably predict the right answer. Each factor moves the score up or down from a neutral 50. SaaS spend matters because per-seat pricing eventually crosses the line where the amortized cost of a build is lower than the SaaS bill. Integrations matter because each one is either a connector subscription or middleware contract you can collapse by owning the integration layer. Blocked workflow features matter the most — they're the signal that you're already paying for customization that doesn't fit, and they're the leading indicator that custom will outperform. Data sensitivity matters because owning the data plane is a strategic asset for any regulated workload. Team size matters because build payback scales with how many people the tool serves. And the 3-year TCO delta matters because numbers, ultimately, are how this decision gets approved.

When to build

High score (80+) cases share three things. First, your workflow is uniquely yours — you've already paid for SaaS customization that doesn't quite fit, and you have a documented list of 5+ features the platform can't deliver. Second, your spend on SaaS plus customization plus middleware is north of $5,000/month, which puts amortized build cost in striking distance. Third, you have integration depth — three or more systems this tool must talk to, where each one is a connector subscription or a brittle Zap that breaks in production. When all three line up, custom usually wins by year 2 and the gap widens from there. The clearest signal is when leadership has already greenlit a “feasibility study” — that's your sign the decision has been informally made and you're collecting the math to defend it.

When to buy

Low score (under 25) cases also share three things. Small teams (under 10 active users). Modest SaaS spend (under $1,000/month). And a workflow that's commoditized — what you're doing isn't different from what every other company in your industry is doing, so the platform's default workflow is good enough. In these cases the SaaS economics work in your favor and the cost of building is straight-up overkill. We tell teams in this range to stay on the SaaS and revisit when something material changes — team size doubles, SaaS bill jumps 20%+ at renewal, or a critical workflow feature gets blocked. Our guide to choosing a software development company walks through how to know when the decision has actually flipped.

The hybrid sweet spot

Scores in the 40-65 range are the most interesting. Full custom is overkill, but you've hit real friction with the SaaS. The right play is a hybrid: keep the SaaS for what it's good at (auth, standard CRUD, baseline reporting) and build custom on top for the 2-3 workflow features that are uniquely yours. We see this most often in mid-market RevOps stacks — the team has Salesforce or HubSpot doing the system-of-record work but has built a custom pricing engine, a custom quote-to-cash flow, and a custom onboarding tool sitting on top. That hybrid layer is where we spend a lot of our build time. It captures the customization upside without the full replatform cost.

The decision factors that don't show up in the score

The calculator's score is honest but not complete. Three soft factors swing real decisions and don't fit cleanly into a number. First, in-house engineering capacity — if you have a 2-person dev team already swamped with the existing roadmap, taking on a custom build means hiring, building, or buying engineering time. Second, vendor lock-in — owning your data and your codebase has strategic value that compounds as your business gets bigger and your switching cost gets higher. Third, customer-facing differentiation — when your workflow is part of how you sell, custom lets you ship features your competitors literally cannot, which is hard to put a dollar value on but very real. The 20-minute scoping call we offer is where we walk through these soft factors and turn them into rough sensitivity adjustments on the score.

What “build” actually costs in 2026

Build costs have stabilized in the last 2 years. A production-grade internal tool for a 25-50 person team runs $45K-$120K for the initial build, with 18% annual maintenance. A serious customer-facing SaaS product is $120K-$400K initial, same maintenance ratio. Stripe-heavy or payment-driven products land in a similar range — see our Stripe integration cost calculator for that specific case. The calculator above uses $1,500/seat + integration cost + blocked-feature cost as its build baseline with a 1.0-1.25x data-sensitivity multiplier, and a $35K floor for the smallest scopes. These are anchored on our recent project data and they line up reasonably well with industry surveys from Capterra and G2 build-vs-buy reports. The mid-point is what we'd quote on a scoping call before any deep discovery.

How to pitch the result internally

The downloadable PDF version of this calculator includes a 1-page CFO memo template. The structure is straightforward: today's 3-year SaaS TCO, projected 3-year custom TCO, payback period, decision score with context on why, and three risks plus mitigations. That format works because it gives the CFO a number to scrutinize, a recommendation to react to, and an exit ramp if the numbers don't hold up. Use the PDF as a starting draft and tune the language to your leadership's communication style. If you want a second pair of eyes on the memo before you send it, drop us a note via the contact page and we'll look at it.