Build vs Buy Software Calculator

Building brings control and differentiation but carries upfront build, ongoing maintenance, and delay cost while you ship. Buying spreads cost as subscription and often launches faster, but may limit customisation and creates vendor dependency.

This calculator compares total build (initial + maintenance × years + time-to-market cost) with total buy (monthly subscription × 12 × years) on the same horizon.

Building brings control and differentiation but carries upfront build, maintenance, and delay cost while you ship. Buying spreads subscription cost and often launches faster, but may limit customisation and create vendor dependency.

This calculator compares total build (initial + maintenance × years + delay) with total buy (subscription × 12 × years).

Use with cost per feature calculator when the decision is one module, RICE prioritisation calculator when the question is roadmap order, and software vendor TCO procurement calculator when the buy path needs implementation, migration, review, renewal, and exit cost detail.

Build side: £85,000 initial + £54,000 maintenance (3 × £18,000) + £25,000 delay cost = £164,000 total.

Buy side: £4,200 × 36 months = £151,200 over 3 years.

On pure cost, buy is cheaper by ~£12,800 — but build may still win if the software is core IP, needs deep integration, or subscription price rises sharply after year three.

Build: £85,000 initial + £54,000 maintenance (3 × £18,000) + £25,000 delay = £164,000 total.

Buy: £4,200 × 36 months = £151,200. Buy is cheaper by ~£12,800 on pure cost in this horizon.

If subscription price rises 20% after year three, long-run buy cost may exceed build — extend comparison period.

Regulatory control, data ownership, and competitive moat can justify higher build cost. Conversely, non-core tools often should not be engineered in-house.

Model subscription price escalation and internal team opportunity cost not captured in maintenance line. If you are already comparing vendors, implementation fees, migration, training, review work, and exit costs, use the software vendor TCO procurement calculator for the buy-side detail.

Core IP, regulatory control, or deep workflow integration may justify higher build cost even when subscription looks cheaper on a three-year horizon.

Non-core tools — CRM, expense, standard analytics — often should be bought to preserve engineering focus on differentiation.

Model internal team opportunity cost in maintenance if engineers on build could ship revenue features instead.

Ignoring maintenance and upgrades on custom code. Comparing one-year buy cost with multi-year build without matching horizon.

Underestimating time-to-market revenue lost while building.

Zero delay cost on build when launch slips 6 months of revenue — enter realistic delay or opportunity cost.

Ignoring vendor price escalation at renewal — rerun buy side at +15% year 4 subscription.

Building because “we can” when cost per feature calculator shows negative ROI on the only differentiator.

Build total = initial build + (annual maintenance × years) + time-to-market/delay cost.

Buy total = monthly subscription × 12 × years compared.

Delay cost captures revenue or efficiency lost while building — enter zero if immaterial.

Exit cost — data migration, contract lock-in, and renewal price escalation on buy side.

Security and compliance fit — vendor SOC reports vs your own control on build.

Roadmap dependency if vendor deprioritises your use case or region.

Hybrid — buy core platform, build thin differentiator on top via API.

Phased build — buy now, build later when revenue funds custom work without runway risk.

Buy core, build differentiator — CRM off-the-shelf, custom quoting on top — splits build vs buy across modules; compare each module's horizon separately.

Buy now, build later when revenue cannot fund £85k build today but subscription is affordable — model year 1–2 buy only, year 3+ build with expected revenue.

Include integration and migration in buy total — year-one professional services often add 25–40% to subscription on enterprise tools.

Rerun when subscription renewal price changes or internal maintenance cost drifts up.

Model hybrid paths — buy core, build differentiator — when neither total wins clearly.

Include migration and integration in buy side before signing multi-year contracts.

Buy-side quotes often show subscription only — add implementation, training, data migration, and internal PM hours. A £40,000/year SaaS can become £120,000 all-in in year one while build shows £200,000 engineering — the crossover may sit in year three, not month one.

Build carries ongoing maintenance, security patches, and key-person risk — model 15–25% of initial build cost annually for maintenance unless you have a dedicated platform team with spare capacity.

Regulatory or data-residency requirements can flip the decision independent of spreadsheet totals — factor compliance audit cost on buy side and legal review on build side.

When the gap is narrow, prefer buy for commodity (auth, email, analytics) and build for differentiated workflow — hybrid totals often beat pure build for speed without surrendering moat.

Model contract exit fees, data export hours, and re-integration cost if the vendor raises prices 20% at renewal — buy decisions look cheaper until year four without exit math.

Ask vendors for reference customers who switched away — their migration story is often more informative than the sales deck ROI slide.

This page should target build vs buy software calculator, build or buy software, software total cost of ownership, custom software vs SaaS, and build vs buy decision searches.

It compares initial build cost, annual maintenance, subscription cost, comparison period, and delay cost. It does not score security, procurement, implementation effort, integration complexity, vendor risk, data migration, compliance, or opportunity cost unless you add those into the entered costs. For deeper buy-side TCO, use the software vendor TCO procurement calculator.