AI is useful for explaining financial terminology, summarizing a broker statement, or helping an investor spot questions to investigate. But Canadian adjusted cost base is a poor place to let a conversational model become the final calculator. The answer depends on a complete, chronological record and rules that must be applied consistently every time.
Consider a Canadian investor who owns the same ETF at two brokerages. For tax purposes, identical securities held by the same taxpayer in non-registered accounts belong to one pooled adjusted cost base. Each broker sees only its own account, so neither institution can reconstruct the whole pool. A chatbot has an additional problem: unless every transaction and adjustment is supplied in a structured form, it cannot know what is missing.
The same issue appears with USD trades. The purchase and sale generally need to be converted to Canadian dollars using the exchange rate for each transaction date. ETF return of capital can reduce ACB, while a reinvested distribution can increase it. A DRIP adds both units and cost. A transfer between brokerages should preserve the original cost history rather than create a new purchase. One omitted event can change every later result.
This is where deterministic software matters. The calculation should produce the same result from the same inputs, preserve the source and date of every event, and show the trail behind the final number. If a transfer cost is missing or a transaction cannot be interpreted safely, the system should raise a warning instead of inventing a confident answer.
AI can still be valuable around that core. It can explain why T5008 Box 20 adjusted cost base differs from an investor's own records, translate a warning into plain language, or help categorize an unfamiliar broker description for review. The important boundary is that AI assists the investigation; it does not silently rewrite the ledger or replace source documents.
That boundary shaped myCostBase, an adjusted cost base tracker for Canadian investors. It pools identical securities across taxable brokerages, applies transaction-date Bank of Canada FX rates, records ETF adjustments, and reconciles the resulting ledger with T5008 slips. The calculation remains inspectable rather than being presented as an unexplained AI answer.
The broader lesson applies well beyond tax software: use language models where interpretation and explanation help, but keep regulated or high-consequence calculations inside deterministic systems with validation, provenance, and an audit trail.
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