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Free Build vs Buy Calculator Online - TestMu AI (Formerly LambdaTest)
Should you build custom software or buy the SaaS? Enter your team, salaries, and license costs to compare total cost over 1 to 5 years, find the break-even year, and get a clear verdict.
Categories
Developers on the build
Average annual developer salary
Build time (months)
Schedule reality multiplier
Annual maintenance (% of build cost)
Hosting and infrastructure per month
Revenue deferred while building
Currency
SaaS price per user per month
Seats (users)
Annual price increase
One-time purchase and integration cost
Comparison horizon
Building does not pay for itself within ten years at these numbers. Buy the off-the-shelf option and spend the engineering time on your own product.
Break-even: building does not pay for itself within 10 years at these numbers.
What is a Build vs Buy Calculator?
A build vs buy calculator is a decision tool that compares the total cost of building custom software against buying an off-the-shelf SaaS product. It combines developer salaries, build time, and ongoing maintenance on one side with seat prices and renewal increases on the other, then reports totals, a break-even year, and a verdict.
The stakes are real on both sides: the average organization now spends about $4,830 per employee per year on SaaS per Zylo's 2025 index, while custom builds routinely blow their budgets. This calculator makes both risks visible before you commit either way.
How does the Build vs Buy Calculator work?
Unlike most build vs buy tools, every assumption here is visible and adjustable. All processing happens in your browser. No data is uploaded. Here is the math:
- Build cost: developers x fully loaded monthly cost x build months x the reality multiplier. The default $133,000 salary is the US Bureau of Labor Statistics median for software developers (May 2024), and the 1.4x loading reflects benefits at roughly 30 percent of compensation per BLS data. Monthly hosting and any revenue deferred while building are added on top.
- Reality multiplier: McKinsey and Oxford research on 5,400 large IT projects found 45 percent average budget overruns, so estimates can be inflated by 1.5x or 2x.
- Maintenance: a recurring 10 to 25 percent of the initial build cost per year (default 18 percent), the widely used industry rule of thumb.
- Buy cost: seats x price x 12, compounded by the renewal increase each year (default 8 percent), plus any one-time switching cost.
- Break-even and verdict: the calculator finds the first year cumulative buy cost overtakes cumulative build cost, and maps it to a four-tier verdict from Build to Buy.
How to use the Build vs Buy Calculator?
Getting a verdict takes about 60 seconds and requires no signup. Follow these steps:
- Describe the build: Enter how many developers the project needs, their average annual salary, the estimated build time in months, a reality multiplier for overruns, plus monthly hosting and any revenue deferred while building.
- Describe the buy: Enter the SaaS price per user per month, the number of seats, the expected annual price increase, and any one-time switching cost.
- Pick the comparison horizon: Choose a 1, 3, or 5 year window. The panel updates instantly with the total cost of building versus buying over that period.
- Read the verdict and break-even year: The calculator names the cheaper path, shows both totals as bars with a five-year cumulative cost chart, and reports the year in which building pays for itself, if it ever does.
- Copy or download the report: Use the copy and download icons beside the result panel to export a Markdown summary of your inputs, totals, and verdict.
What does the research say about build vs buy?
Most build vs buy content quotes unlabeled industry data. These are the figures with real sources behind them:
- 45 percent over budget: large IT projects run 45 percent over budget, 7 percent over time, and deliver 56 percent less value than predicted, per the McKinsey and Oxford study of more than 5,400 projects; 17 percent go badly enough to threaten the company.
- $4,830 per employee: average annual SaaS spend in 2025, up 21.9 percent year over year, per Zylo's SaaS Management Index across $40 billion in managed spend.
- $133,080 median developer wage: the US Bureau of Labor Statistics figure for software developers as of May 2024, before the roughly 30 percent benefits load.
- 15 to 20 percent maintenance: the recurring annual share of the initial build cost that industry practice allocates to bug fixes, patches, and upgrades; a rule of thumb rather than a single study.
- Only 31 percent of projects succeed: the Standish Group's CHAOS 2020 database of 50,000 projects, as reported by independent reviewers, found half of projects challenged and 19 percent outright failed.
Difference between building and buying software
The numbers decide most cases, but the two paths also differ structurally. Weigh these dimensions alongside the totals:
| Dimension | Build (custom) | Buy (SaaS) |
|---|---|---|
| Upfront cost | High, paid before any value ships. | Low, spread across the subscription. |
| Time to value | Months, plus overrun risk. | Days to weeks. |
| Customization | Unlimited, it is your code. | Bounded by the vendor's roadmap. |
| Ongoing burden | Maintenance, security, and upgrades are yours. | Vendor handles them; you absorb price increases. |
| Exit risk | Key-person and tech-debt risk. | Vendor lock-in and migration cost. |
Use cases of the Build vs Buy Calculator
Run the numbers whenever a team proposes building something a vendor already sells. Common situations include:
- Internal tools: price a proposed admin panel, dashboard, or workflow tool against the SaaS that already does it, and attach the report to the decision doc.
- Test infrastructure: QA teams weighing an in-house device lab and browser grid against a cloud platform can model the hardware, maintenance, and staffing as the build side; TestMu AI's cloud offers 10,000+ real devices and 3000+ browsers through Real Device Cloud as the buy side.
- AI agent projects: after picking a framework with the AI Agent Stack Picker, compare building the agent against buying a vertical SaaS agent product.
- Renewal negotiations: bring the build alternative's real cost into a SaaS renewal conversation; a credible build option is leverage even if you never build.
- Budget planning: pair it with the Meeting Cost Calculator and the Percentage Calculator when preparing engineering cost reviews.
Frequently Asked Questions (FAQs)
How do you decide between building and buying software?
Compare the total cost of building, including maintenance, against the subscription cost over three to five years. A common rule is to build only when the investment pays for itself within three years, and to weigh customization needs, data control, and vendor lock-in alongside the raw numbers.
How is the build cost calculated?
Build cost equals developers multiplied by their fully loaded monthly cost and the build time in months, times a reality multiplier for overruns. The default salary of $133,000 reflects the US Bureau of Labor Statistics median wage for software developers as of May 2024.
What is the reality multiplier?
It inflates the build estimate to account for schedule overruns. Hofstadter's Law jokes that work always takes longer than expected, and McKinsey and Oxford research on 5,400 large IT projects found they run 45 percent over budget on average, so multiplying an optimistic estimate by 1.5 to 2 is prudent.
How much does software maintenance cost per year?
A widely used industry rule of thumb puts annual maintenance at 15 to 20 percent of the initial development cost, covering bug fixes, security patches, dependency updates, and small enhancements. This calculator defaults to 18 percent and lets you adjust from 10 to 25 percent.
Why does the SaaS cost grow each year in the calculator?
SaaS list prices and per-seat contracts typically rise at renewal. Industry observations put annual increases around 5 to 10 percent, so the calculator compounds the subscription at 8 percent per year by default. You can set the escalation to zero if your contract locks pricing.
Is my cost data uploaded to a server?
No. All processing happens in your browser. The salaries, seat counts, and license costs you enter never leave your device, and nothing is stored between visits. You can model real budgets without sharing them with TestMu AI or any third party.
Is the Build vs Buy Calculator free to use?
Yes. The Build vs Buy Calculator is completely free, with no signup, no email gate, and no usage limits. Every feature, including the break-even analysis and the Markdown report export, is available to everyone. It is maintained by TestMu AI as part of its free online tools collection.
When should you build instead of buy?
Build when the software is your product or a core differentiator, when no vendor covers your workflow, or when SaaS spend at your seat count clearly exceeds the build and maintenance cost within about three years. Buy when a solved category exists and your engineers have higher-value work.
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