ADR-012: TOMS Tax Deferral to Phase 3 (FinancialLedger)

Status: ✅ Approved — 2026-04-10 Origin: Kalkulations-Engine ProtocolResolves: SB-2 (§ 25 UStG per-line tax split) Impacts: schema-backoffice.md §price_matrices, PRODUCT_domain-model.md §PriceMatrix, Commerce checkout flow

---

Context

The Legal Problem

Under § 25 UStG (TOMS — Tour Operator Margin Scheme / Margenbesteuerung), the tax authority does not calculate VAT per ticket or per line item. Instead, the system computes it on the aggregate margin of the entire departure:

TOMS margin = total_revenue − total_Fremdleistungen (third-party procurement costs)
TOMS VAT    = margin × 19/119

This depends on:

1. Actual fixed costs — vendor invoices that may arrive weeks after the trip
2. Final passenger counts — cancellations and no-shows alter the per-pax cost allocation

The system does not know either value at PriceMatrix generation time.

The Previous Approach (v1/v2)

Earlier iterations of the PriceMatrix spec attempted per-variant tax estimation using total_net_cost / break_even_pax as a proxy. This produced a numeric tax_amount on every variant.

Why this fails:

• The result is a legal fiction — per-variant TOMS tax has no basis in § 25 UStG
• Displaying fictitious tax line items in B2C invoices creates compliance risk
• Every cost change, cancellation, or no-show invalidates the estimation
• The Steuerberater would reject these figures during Nachkalkulation

Standard VAT Has No Problem

Under STANDARD_VAT (no third-party procurement), the tax uses a simple net-back: gross × 19/119. This approach works per variant and requires no deferral.

Decision

1. Tax Resolution by Strategy

Tax Strategy	tax_amount	net_price	Rationale
STANDARD_VAT	Computed: gross × 19/119	Computed: gross − tax	Standard net-back. Legally correct per variant.
MARGIN_SCHEME_25	null	= gross_price	Tax deferred to Phase 3. Customer pays full gross.

IMPORTANT

net_price under TOMS equals gross_price — it does not use null. Commerce needs a non-null price for cart totals, payment capture, and Mollie integration. The system defers tax decomposition, not the sellable price.

2. Phase 3 Authority

The FinancialLedger (Phase 3) is the sole authority for § 25 UStG tax calculation. It computes margin tax at the departure level after the trip, when:

• The operator reconciles actual vendor invoices (Fremdleistungen)
• The system knows final passenger counts
• The operator closes the period

3. Per-Variant DB1 via variable_cost_snapshot

Even though the system defers tax, the PriceMatrix still enables per-variant DB1 (Deckungsbeitrag 1 = revenue − variable costs per ticket) via the variable_cost_snapshot field on each PriceVariant. This gives dispatchers immediate revenue-minus-variable-cost visibility without pretending to know the tax.

DB2 (DB1 − allocated fixed costs) remains a departure-level concern computed by the Backoffice margin calculator.

4. UI Presentation

• TOMS tours display gross_price with "inkl. MwSt." labeling (legally required for B2C gross prices in Germany)
• Backoffice Dispatcher UI shows the "Seats to Break-Even" progress bar (current_booking_count vs. break_even_pax) instead of misleading per-ticket margin numbers
• Tax columns in the dispatcher pricing view show "~" or "nach Abschluss" for TOMS departures

Consequences

Positive:

• Eliminates the risk of displaying fictitious per-ticket tax estimates in invoices
• Legally correct: the system computes § 25 UStG where it should — at departure-level aggregate
• Simplifies Commerce: no need to handle tax recalculation on booking changes
• FinancialLedger has full actual data (invoices + passenger counts) for accurate tax
• Per-variant DB1 remains available for operational visibility

Negative:

• Commerce cannot display a tax breakdown for TOMS tours — only "inkl. MwSt." (this is legally correct anyway)
• Dispatchers see deferred tax indicators instead of estimated margins (mitigated by break-even progress bar)
• Phase 3 (FinancialLedger) becomes a hard dependency for complete financial reporting

Neutral:

• Standard VAT tours remain unaffected — they continue to show full tax decomposition
• B2C customers see no difference — all German prices display as gross ("inkl. MwSt.") regardless

Resolves:

• SB-2 (§ 25 UStG per-line tax split) — deferring to the appropriate level fully resolves the strategic blind spot