Tax logic engine¶


ID	`MOD-092`
System	SD06
Repo	`bank-risk-platform`
Build status	Not started
Deployed	No

What it does¶

MOD-092 is the tax logic engine. It applies NZ and AU GST rules, income tax rules, and expense deductibility rules to the classified transaction portfolio, producing real-time tax position summaries and period-end filing-ready outputs.

NZ GST¶

For sole traders and SMEs registered for GST, MOD-092 accumulates: - Output tax: GST collected on taxable sales (relevant for businesses with invoicing) - Input tax credits: GST claimable on business expenses

The engine produces a quarterly GST return summary — gross sales, total purchases, GST on sales, GST on purchases, and net GST payable or refundable — ready for customer review and (in Phase 4) direct IRD lodgement via the myIR API.

AU GST / BAS¶

For AU entities, MOD-092 produces the Business Activity Statement inputs: G1 (total sales), G11 (non-capital purchases for creditable purposes), and the net GST position. Phase 4 target: direct ATO SBR2 lodgement.

Expense deductibility¶

Each classified transaction receives a deductibility flag from MOD-088. MOD-092 applies the tax rules that determine whether the classification translates to a deductible expense: - Business meals: 50% deductible (entertainment rules) - Home office: apportioned by use - Vehicle: logbook method or kilometre rate - Commute: not deductible

For property expenses, deductibility is assessed in conjunction with MOD-094 and MOD-095 (property attribution and ring-fencing).

Provisional tax estimation (NZ)¶

For sole traders, MOD-092 maintains a rolling provisional tax estimate based on year-to-date classified income and deductible expenses. This is surfaced in the app as a running figure, updated after each classified transaction.

Design phase¶

This module is in design. Build begins in Phase 3 of the Expense Intelligence Platform. See the Expense Intelligence Platform summary for the full implementation roadmap.

Module dependencies¶

Depends on¶

Module	Title	Required?	Contract	Reason
MOD-088	Expense classification engine	Required	`contract/events/`	Classified transaction output from MOD-088 (including tax treatment dimension) is the primary input to tax position calculation.
MOD-094	Property attribution engine	Optional	`contract/events/`	Property-level P&L and deductibility context from MOD-094 is consumed when assessing property expense deductibility — MOD-092.md specifies this is assessed in conjunction with MOD-094 for property expense treatment.

Required by¶

Module	Title	As	Contract
MOD-093	Accounting mapper	Hard dependency	`contract/events/`
MOD-095	Ring-fencing logic engine	Hard dependency	`contract/events/`

Policies satisfied¶

Policy	Title	Mode	How
PRI-001	Privacy Policy	`LOG`	Tax position calculations and deductibility determinations reference personal financial data; all computation inputs and outputs are logged for data minimisation audits.

Capabilities satisfied¶

Capability	Title	Mode	How
CAP-136	CAP-136	`CALC`	Applies NZ and AU GST, income tax, and expense deductibility rules to classified transactions; produces quarterly GST return summaries and provisional tax estimates for sole traders and SMEs.

Part of SD06 — Snowflake Analytics & Risk Platform Compiled 2026-05-22 from source/entities/modules/MOD-092.yaml