How Bilby works
Completion protection and construction insurance
Budget the premium, not the protected amount
Bilby estimates the purchase cost of completion protection and a separate construction/new-build insurance allowance. Completion protection concerns specified extra costs if the contractor cannot fulfil the agreement. The amount protected by a policy is not its premium. A percentage describing legal cover must never be added to the budget as though it were an insurance price.
Reconcile existing cover
Check the actual contract: a supplier or contractor may already provide some cover. The completion-protection reference is a premium reserve, not an insurer quotation. Construction insurance has its own procurement reserve; it excludes annual household insurance after the build and the completion premium counted elsewhere. Neither row demonstrates that a policy exists or that the project is insured.
Where completion protection is required, the statutory minimum protected amount is 10% of the agreed price for the covered work. This is a cover requirement, not Bilby’s premium rate. Boverket
Premium assumptions
The contract value must describe the work to be protected, not simply the land plus every project expense.
| Input | Values | Origin |
|---|---|---|
| Covered contract value | SEK supplied by the user/project | Actual scope input if known |
| Premium fraction | 0.3% / 0.6% / 1.2% | Bilby model assumption |
| Minimum premium reserve | SEK 7,000 / 12,000 / 20,000 | Modelled minimum |
| Unknown-value reserve | SEK 10,000 / 20,000 / 45,000 | Provisional fixed amount |
| Construction/new-build insurance | SEK 10,000 / 25,000 / 50,000 | Separate fixed allowance |
Percentage, minimum or missing-input reserve
When a positive valid covered contract value is supplied, each completion-protection scenario is max(contract value × fraction, minimum). A supplied zero covered value gives zero rather than the minimum. If the value is missing, use the disclosed reserve instead of inventing a contract value. Existing project or actual/manual prices take precedence over a missing-price reference. Low/high describe alternative premium assumptions, not measured insurer risk probabilities.
Fictional covered contract
For SEK 3,000,000 of covered work, the low/expected/high calculation is max(9,000, 7,000), max(18,000, 12,000), max(36,000, 20,000): SEK 9,000 / 18,000 / 36,000. A separately required expected construction-insurance allowance would bring the two-row expected sum to SEK 43,000. This example does not say that cover of SEK 300,000 costs SEK 300,000.
What changes the result
A different covered value changes the percentage calculation until a minimum binds. Contractor, project type, insurer terms and exclusions affect a real offer but are not individually priced here. Missing contract data produces a reserve; changing house appearance does not create a personalised insurer rate. Replace the reserve with the actual premium and reconcile cover already included.
Review and evidence
Price method: Bilby reference-cost V1, researched 16 September 2026. Premium fractions are Bilby assumptions; no universal premium schedule is claimed. The legal cover distinction was checked against Boverket on 18 October 2026, alongside the code review. GarBo completion insurance GarBo new-build insurance
The review date covers this explanation and its implemented method. Price and data dates are stated separately in the article.