Why open-book costing matters for Swiss SMEs
In many Swiss SMEs, procurement costs represent a significant share of revenue — often between 30% and 60% in manufacturing, but also substantial percentages in trade, services and the food sector. When a supplier becomes strategic — by volume, technical criticality or operational dependency — negotiation based solely on the final price leaves room for opacity, risks of unilateral price increases and difficulty in planning margins.
Open-book costing (OBC) is a partnership model in which the supplier shares the cost structure in a structured way: raw materials, labour, energy, overhead, target margin. The goal is not to eliminate the supplier's profit, but to align interests: both parties work to reduce avoidable costs and share the benefits, while maintaining a sustainable economic balance.
In Switzerland, where personnel costs, exchange rates and fluctuations in raw materials directly affect competitiveness, OBC offers SMEs a concrete tool for management control — provided it is implemented with contractual discipline, accounting traceability and compliance with competition and data protection rules.
Comparison of supplier negotiation models
Before launching an open-book project, it is useful to compare the most common models in B2B relationships:
| Criterion | Traditional fixed price | Open-book costing | Cost-plus with cap |
|---|---|---|---|
| Cost transparency | None — negotiated final price | High — documented and verifiable breakdown | Partial — base costs visible, fixed margin |
| Adaptation to input variations | Periodic renegotiation, often conflictual | Formula indexed to agreed indices | Automatic recalculation on direct costs |
| Incentive to reduce costs | Low — supplier retains internal savings | High — contractualised gain-sharing | Medium — depends on cap and margin |
| Management complexity | Low | High — requires audit, reporting and governance | Medium |
| Dependency risk | Medium — switching possible with penalties | High — shared know-how, more costly exit | Medium-high |
| Suitability | Commodity purchases, low volume | Strategic suppliers, co-development, long term | Custom projects, job-order processing |
| Accounting impact | Simple recording at purchase cost | Possible periodic adjustments, gain-sharing provisions | Reconciliation of actual vs invoiced costs |
When it makes sense to adopt open-book costing
OBC is not suitable for every supplier. It is worth focusing on high strategic-value relationships:
Ideal cases
- Critical components with few alternative suppliers (e.g. stamping, CNC machining, custom packaging)
- Multi-year contracts with guaranteed volumes and shared investments
- Product co-development where the supplier contributes to R&D and tooling
- Sectors sensitive to external indices: metals, plastics, energy, logistics
- Existing relationships based on trust and stable performance
When to avoid it
- Standardised purchases with a liquid market and public prices
- Suppliers with already compressed margins and limited administrative capacity
- Context of strong commercial conflict or ongoing litigation
- Lack of internal resources to monitor cost data
- Risk of exchange of sensitive information between the supplier's competitors
Anatomy of an open-book agreement
An effective OBC contract precisely defines what is shared, how the price is calculated and how savings are allocated:
1. Cost breakdown sheet (CBS)
Standard document that breaks down the unit price into verifiable items: material (with indexation formula), labour (hourly rate × standard times), machinery (depreciation/hour), energy, shipping, allocated overhead and supplier target margin. Each item must be updated at the agreed frequency — typically quarterly or semi-annually.
2. Pricing formula and reference indices
The price is updated according to objective indices: LME for metals, chemical/plastics indices, national or cantonal wage indices (e.g. SECO wage index) for Swiss labour, transport indices for logistics. Explicitly define who bears CHF/EUR exchange rate variations beyond a threshold (e.g. ±3%), with reference to an agreed rate or index (e.g. SNB annual average rate).
3. Shared margin and gain-sharing
The supplier's margin remains explicit (e.g. 8–12% on full cost). If a joint initiative reduces costs — process optimisation, scrap reduction, order consolidation — the allocation is defined in advance: for example 60% customer / 40% supplier for the first 24 months, then 50/50. Document every saving with evidence before the split.
4. Audit rights and confidentiality
The contract must provide for the right of verification (audit) on a sample basis, with notice and mutual confidentiality. The supplier's cost data is sensitive commercial information: apply NDA clauses compliant with Swiss law; if processing involves personal data, also observe the FADP (in force since 1 September 2023).
Accounting and tax impact in Switzerland
From an accounting perspective, OBC does not change the recording principle: goods and services purchased are booked at purchase cost (Art. 960a CO and Swiss GAAP FER / relevant accounting standards). The difference lies in managing price adjustments and gain-sharing mechanisms, which require accurate traceability.
Recording invoices with indexed adjustments: if the price varies from the order based on an agreed index, record the invoice at the actual cost and link the variation to the recalculation document (price adjustment note). Avoid undocumented manual reversals: maintain a register of variations by item and period.
Gain-sharing and credits: when the supplier issues a credit for shared savings, account for it as a reduction in purchase cost in the relevant period — not as extraordinary income, unless it is a refund not linked to future purchases. If the saving is offset against subsequent invoices, use a temporary account (e.g. supplier prepayments / discounts receivable) to avoid distorting inventory material cost.
VAT: tax is calculated on the consideration actually due. Price adjustments and credit notes must comply with the requirements of Art. 26 VAT Act (invoice content) and Art. 27 para. 4 VAT Act (receipt document referring to the original invoice); the recipient must adjust the previous input tax deduction, where applicable. For multi-year contracts, verify consistency between periodic invoicing and the total service provided.
Inventory valuation: if the purchase price changes frequently due to indexation, value inventory at weighted average cost (WAC) or FIFO, in line with company policy and Art. 960c CO (lower of cost and net realisable value). Recalculate inventory value when variations are material and document the effect on gross margin in management reports.
Corporate income tax: for corporations (GmbH, Ltd), savings achieved through OBC improve operating results and are taxed normally. No specific tax reliefs apply: efficiency translates into lower cost and higher taxable profit — the benefit is economic, not a direct tax advantage.
Practical implementation in five phases
Selection and prioritisation
Identify the 3–5 suppliers with the greatest impact on cost, quality or supply chain risk. Calculate purchase concentration (80/20 rule) and assess relational maturity. Start with a pilot on a single item or product family.
Transparency workshop
Organise a meeting with the procurement, production and supplier teams. Share forecast volumes, technical specifications and cost targets. The supplier presents the initial CBS; both parties validate assumptions and indices. Document every contested assumption.
Contractualisation
Integrate OBC clauses into the existing framework agreement or draft a dedicated addendum. Define KPIs (OTD, scrap rate, lead time), review frequency, audit rights and exit clauses with notice and orderly transition.
Monitoring and reporting
Establish a quarterly review cycle: CBS vs actual costs comparison, index variations, savings achieved. Link data to the accounting system (Accountex or ERP) via cost centres by supplier and item codes. Produce an updated margin report per SKU.
Continuous improvement
Use OBC data for joint projects: component standardisation, variant reduction, logistics optimisation. Celebrate successes with both teams to strengthen the partnership. Consider extending to other suppliers only after 12 months of a consolidated pilot.
Risks to manage and protective clauses
Open-book costing exposes both parties to specific risks that must be mitigated from the outset of negotiations:
| Risk | Mitigation |
|---|---|
| Artificial allocation of overhead | Agree allocation method (e.g. machine hours) and audit rights; compare with industry benchmarks |
| Dependency and lock-in | Exit clause with 6–12 months' notice; maintain a second qualified supplier for critical items |
| Information leakage | Strict NDA; limit data access to authorised team; penalty clause for breaches |
| Administrative complexity | Standardised CBS templates; automated ERP reporting; review only on variations above threshold (e.g. ±2%) |
| Conflict over savings | Define ex ante the allocation formula, baseline and accepted evidence for each type of saving |
How Accountex supports cost control with open-book suppliers
An integrated accounting system such as Accountex makes it possible to link every supplier invoice to the OBC contract and the relevant CBS. By recording cost centres for strategic suppliers and dedicated item codes, it is possible to track price variations over time and produce automatically updated gross margin reports by product.
Credit notes for gain-sharing are managed with entries linked to the original invoice, maintaining the complete history for audit and review. Variance reports highlight when actual cost exceeds the agreed threshold, signalling the need for a review with the supplier — before the impact is reflected in the year-end financial statements.
For Swiss SMEs that must prepare annual accounts compliant with the Code of Obligations and, where applicable, undergo limited or ordinary audit, this traceability simplifies documentation of price adjustments and justification of inventory value variations — items that auditors and tax authorities may request in case of significant deviations from the previous financial year.
Operational checklist
- ✓Strategic supplier selected with documented cost impact (top 3 by value)
- ✓Cost breakdown sheet validated by both parties with reference indices defined
- ✓Gain-sharing formula and supplier target margin written into the contract
- ✓NDA clauses, audit rights and exit clause agreed
- ✓Cost centres and item codes configured in the accounting system
- ✓Price adjustment and credit note recording process compliant with VAT Act
- ✓Quarterly review calendar with CBS vs actual variance report
- ✓Second qualified supplier identified for items at risk of single sourcing