A government-set rate, published on its own calendar — not the number a currency converter shows for today. The regulation covering entries into the United States is 19 CFR Part 159, Subpart C, read live on 2026-08-31: no rate may be used to convert a foreign-currency invoice for customs purposes other than one the government has itself proclaimed or certified. That single rule is why a buyer's own estimate and the actual duty bill can land on two different numbers for the same shipment.
Set by regulation, not by whatever a bank quotes on the day the parcel actually lands.
The regulation opens with a flat restriction, and it is worth reading exactly as written:
“Except as otherwise specified in this subpart, no rate or rates of exchange shall be used to convert foreign currency for Customs purposes other than a proclaimed rate or certified rate or rates.”19 CFR §159.31, Conversion of Foreign Currency, ecfr.gov, read 2026-08-31
That closes off the obvious shortcut. A bank's rate on the day a check clears, a currency-converter website's rate on the day someone checks, the rate a card network applied to a purchase — none of those are a proclaimed or certified rate under this rule, and none of them is what a foreign-currency invoice actually gets converted at for duty purposes. Only two mechanisms qualify, and the first is used almost never.
The regulation's main mechanism is a quarterly rate, and it names the currencies it applies to directly:
“For the currency of each of the following foreign countries, there will be published in the Customs Bulletin, for the quarter beginning January 1, and for each quarter thereafter, the rate or rates first certified by the Federal Reserve Bank of New York for such foreign currency for a day in that quarter.”19 CFR §159.34(a), Certified Quarterly Rate, ecfr.gov, read 2026-08-31
The list runs to roughly thirty countries, among them Australia, Canada, Denmark, Germany, Hong Kong, India, Japan, Mexico, New Zealand, Singapore, Switzerland, Thailand and the United Kingdom. For every one of those currencies, a single rate is fixed at the start of the quarter and then applies to every shipment exported at any point during that quarter — the regulation's own wording is that the certified quarterly rate “shall be used for Customs purposes for any date of exportation within the quarter,” with two named exceptions covered next.
| Exception | What triggers it | What happens |
|---|---|---|
| Proclaimed rate | The Treasury Secretary proclaims a rate under 31 U.S.C. 5151(b) that does not vary 5 percent or more from the certified daily rate | The proclaimed rate is used for merchandise exported on that date |
| Certified daily rate | The certified daily rate for the actual date of exportation varies 5 percent or more from the certified quarterly rate | The variation is published in the Customs Bulletin and the daily rate is used for that day's shipments instead |
Both exceptions exist to stop a stale quarterly figure from producing an obviously wrong duty bill during a currency swing large enough to matter. Outside either trigger, the quarterly rate is the number in force, even if the market moved in the meantime.
A currency the quarterly list does not name is not left unconverted — it falls to the regulation's fallback rate instead:
“The daily buying rate of foreign currency which is determined by the Federal Reserve Bank of New York and certified to the Secretary of the Treasury … shall be used for the conversion of foreign currency whenever a proclaimed rate or certified quarterly rate is not applicable.”19 CFR §159.35, Certified Daily Rate, ecfr.gov, read 2026-08-31
The same section adds a bank-holiday rule: when the date of exportation falls on a day banks are generally closed in New York City, the certified daily rate for the last preceding business day counts as that day's rate. So even the daily mechanism is not quite the same as checking a live rate at the moment of export — it is the most recent business day's certified figure, one step removed from real time.
A related but distinct figure sits at the US Treasury's own fiscal data site, and it is worth not confusing with the customs valuation rate above:
“The Treasury Reporting Rates of Exchange dataset provides the U.S. government's authoritative exchange rates to ensure consistency for foreign currency units and U.S. dollar equivalents across all reporting done by agencies of the government.”US Treasury, Treasury Reporting Rates of Exchange, fiscaldata.treasury.gov, read 2026-08-31
That dataset is released quarterly and covers the government's own accounting across every agency's foreign-currency transactions, and the page states the Treasury Secretary holds sole authority to set it. It is a real, published, quarterly government rate — but it is not stated on either page read for this guide to be the identical figure Customs and Border Protection certifies under 19 CFR §159.34 for a specific import. Treat the two as siblings with the same quarterly logic behind them, not as one number under two names, unless a specific entry confirms otherwise.
The eCFR is a continuously updated public rendering of the Code of Federal Regulations, not the annually printed edition, and the underlying regulation is administered by US Customs and Border Protection. Country lists and thresholds inside it change only through formal rulemaking, but check the current text before relying on a specific country's status.
Not a bank rate or a market rate looked up on the day of entry. Federal regulation states that no rate may be used to convert foreign currency for customs purposes other than a proclaimed rate or a certified rate, and those rates are set by the government on their own schedule, not pulled from a currency converter.
For most listed currencies, no — quarterly. The regulation names roughly thirty countries, including Canada, the UK, Japan, Mexico and Australia, for which one rate is certified for the whole quarter and used for any date of exportation inside it, unless a daily-rate override applies.
Yes, in one specific case. If the certified daily rate for the actual date of exportation varies by 5 percent or more from the certified quarterly rate, the regulation requires that variance to be published and the daily rate used instead for that shipment. Outside that trigger, the quarterly rate holds for the full quarter.
The certified daily rate applies instead — the daily buying rate the Federal Reserve Bank of New York determines and certifies to the Treasury. If the date of exportation falls on a day New York banks are closed, the regulation directs using the last preceding business day's certified rate.
Because the two numbers are answering different questions. A currency converter shows today's market rate; the rate a shipment is actually valued at was fixed for the whole quarter it was exported in, sometimes months before or after that day's market number, and only moves off that quarterly figure when the 5 percent daily-rate trigger fires.