Build or buy
Should we buy this tool or build it ourselves?
Both options costed over the same horizon, with the user count above which building becomes cheaper.
- ≈ 3 min
- Free calculation · AI commentary on request
- You leave with: Both options costed and the point where building pays
The capability to decide on
Used only for the commentary. It enters no calculation.
The ones who will genuinely use it — not the ones with access.
The longer the horizon, the more maintenance weighs on the build option.
At this user count, buying costs less. The fixed cost of building does not amortise yet.
The result
The figures above are computed and free. If you also want them read back to you — what they mean, what is specific to your sector, where to start — that is produced on request.
Cumulative cost, month by month
Building starts high and rises slowly; buying starts low and climbs linearly. Where the two lines cross is the real answer to the question.
The breakdown
The production-hardening multiplier is the line that decides most of these calls, and the one no initial estimate contains.
| Line | Estimate |
|---|---|
| Set-up | |
First working version 35 engineering days to something that works in a demo. | €31,500 €9,000 — €98,000 |
Production hardeningoften omitted Auth, error handling, evaluation, monitoring, data retention, accessibility. Multiplies the first version by 2.0 — the most reliably underestimated multiplier in software. | €31,500 €3,600 — €215,600 |
Vendor set-up and integrationoften omitted Rarely zero even when the sales deck says so: someone still configures SSO, maps the data and trains the admins. | €4,500 €1,200 — €16,800 |
| Recurring | |
Maintenance (36 months)often omitted Higher than ordinary software: model versions are retired on the provider's schedule, not yours. | €56,700 €7,560 — €423,360 |
Inferenceoften omitted €5/active user/month × 40 × 36 months. Negligible per unit, never zero. | €7,200 €1,440 — €28,800 |
Licences (36 months) €30/seat/month × 40 users × 36 months. | €43,200 |
Sensitivity of the build option
The buy cost tracks the market price closely; the build cost rests on several bets at once. Here is which one to check first.
Each assumption is moved ±20% on its own, holding the others fixed. The longest bar is the one worth checking first — not necessarily the one that felt most uncertain.
The assumptions
Every figure above rests on these. The ones marked “assumption” have no external source: they are modelling choices, labelled so they can be argued with rather than mistaken for measurements.
- Complexity MediumObserved
- 15–70 engineering days to a first version.
- Production hardening × 2.0Observed
- Authentication, error handling, evaluation, monitoring, data retention, and the accessibility and audit requirements a demo never has. The most reliably underestimated multiplier in software.
- Annual maintenance 30 %Assumption
- Higher than conventional software maintenance because model versions are deprecated on the provider's schedule, not yours.
- Inference 5 €/user/monthAssumption
- API inference for a moderately used internal feature. Cheap per unit and easy to forget entirely.
What the calculation does, what the AI does
Every figure on this page comes from a deterministic algorithm running in your browser: the same input always gives the same result, and nothing is sent to produce it. AI runs only afterwards, to write the commentary from those figures. It produces none of them — the format it fills has no numeric fields — and any sentence quoting a value the calculation did not produce is removed before display.
Where to go next
See all 19 tools →- Cost calculator
What does our AI transformation actually cost, and when does it break even?
≈ 3 min · A line-by-line budget, the return and the break-even month - Use-case prioritisation
Of all our ideas, which one first?
≈ 5 min · Your use-case list ranked, on a value/effort plane - Right-size licences
How many seats are we paying for nothing?
≈ 2 min · The saving available at renewal, and the tiered arrangement - Inference cost
What will the model calls cost once in production?
≈ 3 min · The monthly bill and its two-year trajectory - Internal team or external
From when is hiring cheaper than buying days?
≈ 3 min · The crossover month and how many hires are justified - Automate a process
Is this process worth automating, and how many months until it pays back?
≈ 3 min · A signable automation case, with a proposed decision