Customs exchange rates are not market rates

When an invoice is in a foreign currency, customs does not use the rate your bank charged. Each administration publishes its own rate on its own schedule, and that rate is the legal one for valuation.

• United Kingdom — HMRC publishes monthly rates, fixed in advance, that apply for the whole calendar month of the declaration.
• European Union — the ECB reference rate published on the second-last Wednesday of a month applies for the whole following month (Implementing Regulation (EU) 2015/2447, Article 146). Non-euro member states publish national rates.
• Australia — the Australian Border Force publishes daily rates; the rate on the day of export applies, not the day of arrival.
• New Zealand — NZ Customs sets fortnightly rates, published 11 days ahead; the rate for the period in which the entry is lodged applies.
• Japan — Japan Customs publishes weekly rates based on the average market rate of the week two weeks before the declaration.
• United States — CBP uses rates certified by the Federal Reserve Bank of New York, quarterly for listed currencies unless the daily rate moves 5% or more. CBP publishes them as notices, not as a data feed.

LandedGrid ingests the official rate where one is published in machine-readable form and labels every conversion with its source and period. Where no official feed exists, or your currency is not listed, you supply the rate and the result is marked “user provided”. A market rate is never presented as a customs rate.