Build or Buy Your ETRM? The Costs That Never Make the Business Case
When a trading firm decides to build its own ETRM, the decision usually comes down to one number: the development budget. It’s visible, finite and easy to approve.
What that number leaves out is everything that happens after go-live: keeping the system correct, secure, compliant and understood, year after year. For an ETRM, that’s where most of the cost sits.
Here are four places it tends to show up.
1. Vibe-coding your mission-critical system
AI coding assistants mean a team can now produce something that looks like a working trading system in days. Speed isn’t the problem. Trust is.
Every trade, position and settlement obligation passes through your ETRM, and its mistakes are rarely loud. A missing fee defaulting rule won’t throw an error; it quietly leaks margin on every transaction until month-end reconciliation catches it.
Then there’s security. Certified vendors are audited every year on how they find and fix vulnerabilities. A vibe-coded system has no such obligation, and your auditors will want to know what covers that gap.
What it costs: leaked margin, audit findings, and security controls you now have to build and prove yourself.
2. The market sets your roadmap
Energy trading rules rarely stay still for long. In 2026 alone, Nordic and Baltic power futures changed clearing houses, REMIT reporting was overhauled, and EU countries faced deadlines on new electricity and gas market rules.
For a firm running its own ETRM, each of those is a project nobody budgeted for, on a deadline nobody inside the firm chose.
What it costs: an engineering team that spends its time keeping up with the market instead of building what the business asked for.
3. The spreadsheet that slowly becomes load-bearing
When the in-house system falls short, spreadsheets creep in to fill the gap: a script that pastes data across, a Power Query that “just works” until someone upgrades Office. Each one is small. Together, they become the actual system people rely on.
And spreadsheets fail silently. Someone overwrites a formula with a hard-coded number, copies multiply, and by the time figures reach a trader or risk manager, no one is sure which version is right.
What it costs: decisions made on numbers no one can fully vouch for, and hours spent double-checking them.
4. The key-person problem
Ask who really understands your in-house ETRM, and the answer is usually two or three names. They know why the settlement logic was written that way, and the workaround for the bug nobody had time to fix. When one of them resigns, that institutional knowledge leaves with them.
What it costs: months of recruiting and onboarding, while the remaining team relearns a system that was never fully written down.
Two decisions, not one
These pitfalls share a root cause: treating the ETRM as one build-or-buy decision, when it’s really two.
Every ETRM runs on two clocks:
Yours: how you price, hedge, optimise and decide. That’s where your competitive edge lives, and it’s worth building.
The market’s: settlement rules, exchange connections and reporting formats, which change whenever regulators and exchanges say so. That’s the core every firm needs, and building it yourself means keeping pace with it forever.
Coral is built around that split. Previse runs the core and keeps it in step with the market, while your team builds its edge on top through Coral’s open REST API and App Ecosystem.
Buy the core. Build your edge.
See where the line falls for you
You don’t have to choose between a rigid legacy platform and the endless maintenance of a custom build. Our guide, Buy the Core. Build Your Edge., shows the third option:
Which ETRM functions belong in the core, and which belong in your edge
What the 2026 deadlines meant for an in-house build vs. Coral
How custom builds, legacy ETRMs and Coral compare on cost, time to go-live, flexibility and upgrades