Cumulative cost over time
BuyBuild
Build it or buy it? Work it out with your own numbers.
Most comparisons stop at licence fees versus a development quote. This one adds what usually decides the matter: user growth, price rises at renewal, setup and integration work, maintenance, time to launch, and eight questions about fit. You get a recommendation, the reasons behind it, and what would change it.
- Free, no sign-up
- Runs in your browser
- The full model is published below
Your decision
The case, laid out
Where the money goes
Why this recommendation
What would change the answer
Risks to deal with first
Before you sign anything, ask
Tick them off as you go. Vague answers are a warning sign in their own right.
Want a second opinion on the numbers?
Send us your inputs and any quotes you have. An engineer will point out what looks off and what we would check before committing. No charge for the first conversation.
Hidden costs
What people forget to put in the spreadsheet
When buying
- Growth in users. Per-user pricing that looks cheap for 20 people can be your biggest line item at 200.
- Renewal price rises. The first-year discount disappears and list price climbs. Get any cap in writing.
- Add-ons and tiers. Single sign-on, audit logs, API access and extra storage are often sold separately.
- Workarounds. When a product fits 70% of the process, people do the other 30% in spreadsheets. That time is a cost.
- Leaving. Exporting data, retraining staff and rebuilding integrations if you ever switch.
When building
- Maintenance. Frameworks age, libraries get security fixes and browsers change. Software that is not maintained decays.
- Time to launch. Every month in development is a month without the system, and first estimates tend to be optimistic.
- Key-person risk. If one developer understands it, you have a dependency, not an asset.
- The unglamorous features. User management, permissions, audit trails, backups and reporting take real time to build.
- Hosting and monitoring. Servers, databases, email, error tracking and someone watching it.
The model
Exactly how the numbers are worked out
No black box. If you disagree with an assumption, change the input or tell us.
- Buying, each monthprice × (1 + renewal rise)year × users × (1 + growth)year + admin. Setup and customisation are added in month one.
- Building, each monthThe build cost lands in month one. After launch: build cost × maintenance ÷ 12 + hosting.
- WaitingEach month before an option is live adds the monthly value you entered to that option's cost.
- Break-evenThe first month when the running total for building drops to or below the running total for buying.
- Fit scoreEach answer scores from −2 (points to buying) to +2 (points to building). The recommendation weighs that score against the cost gap, and building is held back to hybrid if nobody would maintain it.
- ConfidenceHigh when the fit score and the costs point the same way and at least five questions are answered. Low when they conflict or most questions are blank.
Questions
About this tool
Is this a quote?
No. It is a planning model. It shows how the costs behave over time and which way the evidence points, so you go into vendor and developer conversations knowing what to ask. Real quotes will move the numbers; the questions and the break-even logic stay useful.
Where do the default numbers come from?
They are a plausible example for a 40-person team choosing between a per-user SaaS product and a mid-sized custom build. Replace every one of them. The model is only as good as the figures you put in.
Why does it ask what the system is worth each month?
Because time to launch is a real cost. A product can often be live in weeks; a build takes months. If the system would save or earn a meaningful amount each month, the months spent waiting belong in the comparison. Leave it at zero to compare cash costs only.
What does "hybrid" mean in practice?
Buy a product for the common part of the problem, then build the piece that is specific to how you work, usually as an integration, an extension or a small internal app around it. It is often the fastest route to something that fits.
Is my data stored?
The calculation runs in your browser. We keep an anonymous record of the inputs and result, with no name or email, to improve the model. Nothing identifies you unless you ask for the emailed report.
Email me the report
The full comparison with your inputs, the reasoning and the question checklist. An engineer may follow up once; no mailing list.
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