Weighted purchase cost: quantities are the weights, not invoices

Start with the totals

For each lot, multiply quantity by unit price and add the included acquisition fees. Sum lot costs, then divide by total quantity. Keep one row per lot so its price stays tied to its size.

Fees affect what actually left your funds at acquisition. Check which costs the inputs include rather than assuming a quoted price includes everything.

References: Investor.gov — Understanding fees

Do not combine incomparable purchases

Use a common unit and currency. Large and small packs must first be expressed in the same unit, while combining two currencies produces no meaningful cost average without conversion.

An average summarizes the records; it does not replace them. Retain separate invoices and quantities for later inventory tracking or expense review.

A numerical average is not a tax treatment

This calculator aggregates purchases and their fees. Partial sales, returns, changes in unit count and tax-lot methods are not determined by this average.

A lower average alone is not a reason to buy more. It describes the inputs, not whether a decision is suitable or the purchase is worth making.

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