Why the internal tool build vs buy calculator matters
Build-versus-buy decisions go wrong when maintenance is left out: the build is a project with an end date, the maintenance is a salary with none. This page turns that decision into a handful of inputs you can defend in a budget review: volume, unit cost, rate of adoption, and time. The output is a planning baseline, not a promise — it tells you whether the idea deserves a vendor quote, a pilot, or a pass.
- • Biggest swing factor: build cost
- • Second-order factor: annual maintenance as a share of build
- • Often ignored: how much of the vendor's product you would actually use
What actually changes the answer
build cost moves this number first, then annual maintenance as a share of build. Run a conservative case and an upside case before you commit. If the maths only works in the upside case, treat it as a time-boxed test with a kill date rather than a line in next year's plan.
What to do with the result
If payback runs past two years, buy. Build only when the workflow is a genuine competitive difference, not when the vendor is merely annoying.
Related guides
Long-form playbooks on the same topic, written by the RevenueLab editorial team.
FAQ
What does the internal tool build vs buy calculator work out?
It applies Net savings = (hours saved × adoption × hourly rate) − tool cost to the values you enter for licence hours-equivalent avoided per month, loaded engineering hourly cost, ongoing maintenance hours cost per month, initial build cost, share of the vendor's feature set you actually need. Build-versus-buy decisions go wrong when maintenance is left out: the build is a project with an end date, the maintenance is a salary with none.
How accurate is this internal tool build vs buy calculator?
Directional. It captures the cost comparison, not the strategic argument — decide the strategy first, then use this to sanity-check the money. Replace the defaults with your own invoice, usage export, payroll data, statement, or vendor quote before making a commitment — the maths is exact, so the answer is only as good as the inputs you feed it.
Which input should I stress-test first?
build cost. Re-run with a pessimistic value for it; if the decision flips, that assumption is the thing you need real data on before signing anything. After that, check annual maintenance as a share of build and how much of the vendor's product you would actually use.
Which scenario should I start from?
Start with the preset closest to your situation — lean case, expected case, scaled case — then edit the sliders. Presets are realistic starting points, not benchmarks to match, and every change updates the result instantly.
What should I do after running the numbers?
If payback runs past two years, buy. Build only when the workflow is a genuine competitive difference, not when the vendor is merely annoying. A useful planning benchmark to compare against: In-house tools cost 15–25% of build cost per year to maintain.
Can I share or save this calculation?
Yes. Your inputs are written into the page URL, so copying the link shares the exact scenario you are looking at — the person who opens it sees the same numbers. You can also export the inputs and results to CSV or PDF from the result card and keep it with the rest of your workings.
How this calculator is built
Independently maintained
Written by Sam Doshi and the RevenueLab editorial team. We don't sell the data feeds this tool is built on.
Sourced from primary data
Benchmarks come from public AdSense / Stripe / IRS disclosures and reader-submitted data — never third-party "$X per view" claims. Full methodology.
Last editorial review
Reviewed on a rolling quarterly cycle. Dated reviews are published on the methodology record for each calculator.
Editorial standards
See our editorial policy and disclaimer. Results are estimates, not advice.