When to Use

Use this skill when processing vendor invoices, preparing a periodic VAT/GST return, or auditing the indirect tax leakage in a trading entity's cost base across UK HMRC, EU member states, Singapore IRAS and Australia ATO.

The engine:

• Classifies an invoice as EXEMPT, STANDARD_RATED, REVERSE_CHARGE or OUT_OF_SCOPE (assess_invoice_tax).
• Self-assesses both reverse-charge legs — output VAT for UK return Box 1 and the ratio-restricted input tax claim for Box 4.
• Computes the pro-rata recovery ratio with the statutory rounding-up rule applied where it exists (set_partial_exemption_ratio).
• Quantifies unrecoverable input VAT as an expense hitting trading PnL.
• Aggregates a period return summary, keeping every per-invoice determination in summary.assessments for the audit trail (generate_vat_return_summary).

Every assessment carries a warnings tuple naming the determinations the engine could not make from the category alone.

When NOT to Use

• As the place-of-supply analysis itself. The engine assumes the modelled taxable services follow the B2B general rule (VATA 1994 s.7A; Directive Art 44). It flags, but cannot resolve, the immovable-property exception for exclusive-use co-location (CJEU C-215/19 A Oy).
• To split a bundled exchange invoice. Exchange execution may be exempt while membership, port, connectivity and technology charges on the same invoice are standard-rated (HMRC VAT Notice 701/49 para 6.9). The split is a human determination; the engine warns and gives you a category for the standard-rated half.
• Across currencies. No FX conversion is performed. Amounts must be pre-converted to a single currency at the correct statutory rate and date, and the return is filed in the tax jurisdiction's own currency.
• For credit notes, refunds or negative amounts. Rejected by design rather than silently signed through the recovery arithmetic.
• For special methods (PESM), annual adjustments, the capital goods scheme, the UK reg 106 de minimis test, VAT groups, or the Australian reduced input tax credit regime. None are modelled.
• As the Australian apportionment method. The ATO prescribes no turnover pro-rata; GSTR 2006/3 requires a "fair and reasonable" method, with direct estimation preferred.
• As tax advice or a filed return. It produces indicative figures for a tax function to review, not a submission.

Prerequisites

• Python 3.10+, standard library only.
• An accounts payable ledger providing, per invoice: invoice_id, vendor_name, vendor_jurisdiction, entity_jurisdiction, service_category and a VAT-exclusive net_amount_usd, all amounts already in one currency.
• The entity's taxable and exempt turnover for the period, with UK "specified supplies" (exempt Grp 5 services to non-UK customers, SI 1999/3121) counted as taxable.
• A view on whether the entity is entitled to a full input tax credit — this determines whether Singapore's and Australia's reverse charge regimes apply at all.

Workflow

1. Set the recovery ratio first. Call set_partial_exemption_ratio(taxable_supplies_usd, exempt_supplies_usd, rounding) — or pass a known percentage to the constructor. Choose rounding by jurisdiction: UP_WHOLE_PERCENT for UK and EU entities (reg 101(4); Art 175(1)), UP_TWO_DECIMALS where UK reg 101(5) applies (residual input tax over £400,000/month on average), NONE for Singapore and Australia. The default is NONE, so a UK/EU entity that leaves it unset under-recovers.
2. Ingest invoices as TradingExpenseInvoice records. Split bundled exchange invoices before ingestion, booking the standard-rated lines as EXCHANGE_MEMBERSHIP_CONNECTIVITY_FEE.
3. Assess each invoice with assess_invoice_tax(invoice). The order of determination is: exempt financial supply first (an exempt import carries no reverse charge), then the cross-border test, then domestic treatment.
4. Resolve the warnings. Each entry marks something the category could not settle — a bundled exchange invoice, an exclusive-use co-location contract, a Singapore/Australia entitlement question, US sales tax. Clear them before the return is filed; do not treat a warned determination as final.
5. Generate the return summary with generate_vat_return_summary(invoices). Map total_output_vat_usd to UK Box 1 and total_recoverable_input_vat_usd to Box 4, then add output VAT on the entity's own sales — the engine covers the purchase ledger only. Post total_unrecoverable_vat_expense_usd to PnL and retain summary.assessments.

Common Pitfalls

• Treating every exchange invoice as exempt. HMRC VAT Notice 701/49 para 6.9: "Basic admission or membership charges are taxable at the standard rate… The liability of other charges depends on exactly what is being done by the exchange for the charge." Booking the whole invoice as exempt loses the input tax recovery on the standard-rated element.
• Reverse-charging an exclusive-use co-location cage. CJEU C-215/19 A Oy turned on the customer having no exclusive right of use of a defined space. A dedicated cage or suite can flip the supply into the immovable-property rule, taxable where the data centre sits — meaning a local VAT registration obligation, not a reverse charge, and a mis-filed return in two jurisdictions if you get it wrong.
• Assuming the reverse charge is universal. Singapore's imported-services regime and Australia's GST Act Div 84 both apply only where the recipient is not entitled to a full input tax credit. A fully-recovering SG or AU entity is outside them; a UK or EU entity is inside regardless of recovery position.
• Declaring only the net reverse-charge cost. The self-assessed output VAT belongs in Box 1 and the restricted claim in Box 4. Netting them off understates declared output tax even though the cash effect is identical.
• Skipping the statutory rounding-up. A raw 20.4% ratio is 21% under UK reg 101(4) and EU Art 175(1). Using the raw figure systematically under-recovers input VAT.
• Leaving specified supplies out of the numerator. Exempt Grp 5 supplies to non-UK customers carry recovery under SI 1999/3121; parking them in the exempt bucket understates the ratio.
• Assuming 100% recovery on co-location and market data. A trading entity with largely exempt income recovers only its pro-rata share; the rest is a permanent PnL cost, not a receivable.
• Filing in the wrong currency. VAT/GST is declared in the tax jurisdiction's currency. This engine does no FX conversion — a ledger in USD assessed at 20% does not produce a filable UK figure.
• Changing the ratio mid-batch. generate_vat_return_summary applies whatever ratio the engine currently holds, so re-running it after a ratio change silently produces different numbers for the same invoices.

Verification

Run the unit test suite. It covers exempt financial services, the exchange membership split, domestic standard-rated supplies, cross-border reverse charge including the self-assessed output VAT leg and recipient-rate selection, the Singapore/Australia full-credit carve-out, statutory rounding (whole percent, two decimals, the 100% cap and the exact-percentage guard), fail-closed rate lookup for unmapped or non-enum jurisdictions, ratio validation, and return summary aggregation with its audit trail:

python -m unittest discover -s skills/vat-gst-treatment-of-trading-related-services/scripts

Repository-wide checks:

python tools/validate_skills.py
python tools/run_all_tests.py

Related Skills

• transfer-pricing-for-multi-entity-trading-operations
• multi-jurisdiction-tax-residency-implications
• record-keeping-requirements-for-tax-audit-defense
• market-data-entitlement-and-licensing-per-venue
• exchange-fee-tier-and-rebate-structure-analysis