Why Australian importers get this wrong twice
Importing into Australia produces a specific and repeatable accounting mess. The goods are almost always priced in USD, because that is how Chinese and US suppliers quote. Almost every cost after that arrives in AUD: the forwarder invoices locally, customs assesses duty and GST in AUD, and the brokerage fee is an Australian invoice. So a single shipment carries two currencies, and converting the whole thing at one rate is wrong in both directions.
This calculator handles that directly. The goods convert at the rate you set. Each charge carries its own currency, and the ones already billed in AUD are left alone rather than being converted a second time. That one detail removes the most common error in importer spreadsheets, which is applying the exchange rate to a freight bill that was already in dollars.
The second mistake is GST. Import GST is charged on the value of the taxable importation, which is broadly the customs value plus duty plus transport and insurance, so it is not simply ten percent of what you paid the supplier. More importantly, if you are registered for GST you generally claim that import GST back as an input tax credit. Money you get back is not a cost, and putting it into landed cost will understate every margin you calculate from it. Only include GST here if you genuinely cannot recover it.
Duty is a different story. Duty is not recoverable, so it is a real and permanent part of your cost. The rate depends on the tariff classification of the goods and on whether a free trade agreement applies, and Australia has agreements that reduce or eliminate duty on goods from several major sourcing countries. Enter the duty amount from your customs documentation rather than estimating a percentage, and allocate it by value, since value is the basis customs used.
This tool is a costing calculator, not customs advice. It does not classify goods, look up tariff rates, or determine your eligibility for any concession. Use the figures from your broker or your customs entry, and this will turn them into an accurate cost per unit in AUD.