diff --git a/packages/wp-checkout/src/lib/format-value-for-currency.js b/packages/wp-checkout/src/lib/format-value-for-currency.js
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+/* @format */
+
+/**
+ * Format a monetary amount according to the custom of a given locale.
+ *
+ * Displaying monetary amounts depends on
+ *   (1) the currency being displayed; this determines whether or not we need to
+ *       handle a fractional part (e.g. yen) and what symbols to display (e.g. $ and JPY)
+ *   (2) the user's locale; this determines how decimal numbers are formatted and
+ *       how digit groups are displayed for large numbers, as well as the placement of symbols
+ *
+ * Getting this right is an important part of localization.
+ *
+ * The rules for this are not standardized and each region/currency has idiosyncrasies.
+ * This function tries very hard to do the right thing but should default to something sensible.
+ * It is essentially a big switch statement on locale and currency.
+ *
+ * Surprisingly there are no standard documents on country-level currency formatting,
+ * but the following resources are helpful:
+ *     https://www.thefinancials.com/Default.aspx?SubSectionID=curformat
+ *     https://publications.europa.eu/code/en/en-370303.htm
+ *     https://en.wikipedia.org/wiki/ISO_4217
+ *     https://en.wikipedia.org/wiki/ISO_3166-1_alpha-2
+ *     https://en.wikipedia.org/wiki/Currency_symbol
+ *     https://en.wikipedia.org/wiki/Decimal_separator
+ *
+ * @param {string} localeCode ISO 3166-1 alpha-2 region code
+ * @param {string} currencyCode ISO 4217 currency code
+ * @param {number} amount In minor currency units
+ * @returns {string} Formatted monetary amount
+ */
+export default function formatMonetaryAmountForLocale( localeCode, currencyCode, amount ) {
+	// Validate input
+	if ( ! ( typeof locale === 'string' || localeCode instanceof String ) ) {
+		throw 'locale parameter must be a string.';
+	}
+	if ( ! ( typeof currency === 'string' || currencyCode instanceof String ) ) {
+		throw 'currency parameter must be a string.';
+	}
+	if ( ! ( typeof amount === 'number' || amount instanceof Number ) ) {
+		throw 'amount parameter must be a number.';
+	}
+	if ( ! Number.isInteger( amount ) ) {
+		throw 'amount parameter must be an integer.';
+	}
+
+	const absoluteAmount = Math.abs( amount );
+	const amountSign = Math.sign( amount );
+	const normalizedLocaleCode = localeCode.toLowerCase();
+	const normalizedCurrencyCode = currencyCode.toUpperCase();
+
+	switch ( normalizedLocaleCode ) {
+		case 'us':
+			switch ( normalizedCurrencyCode ) {
+				case 'USD':
+					return formatSymbolAmount(
+						amountSign,
+						absoluteAmount,
+						normalizedLocaleCode,
+						normalizedCurrencyCode
+					);
+				case 'JPY':
+					return formatSymbolAmount(
+						amountSign,
+						absoluteAmount,
+						normalizedLocaleCode,
+						normalizedCurrencyCode
+					);
+				case 'GBP':
+					return formatSymbolAmount(
+						amountSign,
+						absoluteAmount,
+						normalizedLocaleCode,
+						normalizedCurrencyCode
+					);
+				default:
+					return formatSymbolAmountCode(
+						amountSign,
+						absoluteAmount,
+						normalizedLocaleCode,
+						normalizedCurrencyCode
+					);
+			}
+
+		default:
+			throw 'Unhandled locale';
+	}
+}
+
+/**
+ * Symbol and amount, e.g. $100.
+ *
+ * @param amountSign
+ * @param absoluteAmount
+ * @param localeCode
+ * @param currencyCode
+ * @returns {string}
+ */
+function formatSymbolAmount( amountSign, absoluteAmount, localeCode, currencyCode ) {
+	const symbol = symbolForCurrency( currencyCode );
+	const sign = amountSign >= 0 ? '' : '-';
+
+	if ( 0 === amountSign ) {
+		return symbol.concat( '0' );
+	}
+
+	return sign.concat(
+		symbol.concat(
+			renderAmountWithSeparatorsForCurrencyAndLocale( absoluteAmount, localeCode, currencyCode )
+		)
+	);
+}
+
+/**
+ * Symbol, amount, and currency code, e.g. $100 NZD.
+ * @param amountSign
+ * @param absoluteAmount
+ * @param localeCode
+ * @param currencyCode
+ */
+function formatSymbolAmountCode( amountSign, absoluteAmount, localeCode, currencyCode ) {
+	return formatSymbolAmount( amountSign, absoluteAmount, localeCode, currencyCode ).concat(
+		' '.concat( currencyCode )
+	);
+}
+
+function renderAmountWithSeparatorsForCurrencyAndLocale(
+	absoluteAmount,
+	localeCode,
+	currencyCode
+) {
+	const { integerPart, fractionalPart } = digitGroupsOfAmountForCurrency(
+		currencyCode,
+		absoluteAmount
+	);
+	const { decimalSeparator, groupSeparator } = separatorsForLocale( localeCode );
+
+	const base = minorUnitsPerMajorUnitForCurrency( currencyCode );
+
+	if ( 1 === base ) {
+		return integerPart.join( groupSeparator );
+	}
+
+	return integerPart
+		.join( groupSeparator )
+		.concat( decimalSeparator )
+		.concat( fractionalPart );
+}
+
+/**
+ * Separate an amount into its fractional part and grouped digits of the integer part.
+ *
+ * @param {string} currencyCode ISO 4217 currency code
+ * @param {number} absoluteAmount Amount in minimal currency units
+ * @returns {object}
+ */
+function digitGroupsOfAmountForCurrency( currencyCode, absoluteAmount ) {
+	if ( ! ( Number.isInteger( absoluteAmount ) && absoluteAmount >= 0 ) ) {
+		throw 'absoluteAmount parameter must be a nonnegative integer.';
+	}
+
+	// Zero money is a special case.
+	if ( 0 === absoluteAmount ) {
+		const fractionalPart = minorUnitsAsDecimalForCurrency( currencyCode, 0 );
+		return { integerPart: [ '0' ], fractionalPart: fractionalPart };
+	}
+
+	const base = minorUnitsPerMajorUnitForCurrency( currencyCode );
+
+	// Currencies with no minor unit are a special case.
+	if ( 1 === base ) {
+		return { integerPart: groupDigits( absoluteAmount ) };
+	}
+
+	const fractionalPart = minorUnitsAsDecimalForCurrency( currencyCode, absoluteAmount % base );
+	const majorUnitAmount = Math.floor( absoluteAmount / base );
+
+	return { integerPart: groupDigits( majorUnitAmount ), fractionalPart: fractionalPart };
+}
+
+/**
+ * Computes the base 1000 digits of an integer as an array of strings from most to least significant.
+ *
+ * @param {number} amount Number to decompose
+ * @returns {array} Base 1000 digits as strings, from most to least significant
+ */
+function groupDigits( amount ) {
+	function groupDigitsAccum( localAmount, localDigits ) {
+		if ( localAmount < 1000 ) {
+			return [ localAmount.toString() ].concat( localDigits );
+		}
+
+		const nextGroup = localAmount % 1000;
+		const remainder = Math.floor( localAmount / 1000 );
+
+		return groupDigitsAccum( remainder, [ nextGroup.toString() ].concat( localDigits ) );
+	}
+
+	return groupDigitsAccum( amount, [] );
+}
+
+/**
+ * Number of minor units per major unit. When expressed as a power of 10 this is called the exponent.
+ * Some currencies have non-integer exponents (e.g. Madagascar) so we return the raw number instead.
+ *
+ * @param {string} currencyCode ISO 4217 currency code
+ * @returns {number} Number of minor currency units per major unit
+ */
+function minorUnitsPerMajorUnitForCurrency( currencyCode ) {
+	const normalizedCurrencyCode = currencyCode.toUpperCase();
+	switch ( normalizedCurrencyCode ) {
+		case 'JPY':
+			return 1;
+
+		case 'BRL':
+		case 'CAD':
+		case 'EUR':
+		case 'GBP':
+		case 'NZD':
+		case 'USD':
+			return 100;
+
+		default:
+			throw 'Unknown currency exponent';
+	}
+}
+
+/**
+ * Formats fractional currency units; different currencies have different customs
+ *
+ * @param {string} currencyCode ISO 4217 currency code
+ * @param {number} absoluteAmount Number of minimal currency units
+ * @returns {string}
+ */
+function minorUnitsAsDecimalForCurrency( currencyCode, absoluteAmount ) {
+	const normalizedCurrencyCode = currencyCode.toUpperCase();
+	switch ( normalizedCurrencyCode ) {
+		case 'EUR':
+		case 'GBP':
+		case 'NZD':
+		case 'USD':
+			return absoluteAmount.toString().padStart( 2, '0' );
+
+		case 'JPY':
+			throw 'Currency does not have a minimal unit.';
+
+		default:
+			throw 'Unknown minor unit format';
+	}
+}
+
+/**
+ * Graphical currency symbol
+ *
+ * @param {string} currencyCode ISO 4217 currency code
+ * @returns {string} Currency symbol
+ */
+function symbolForCurrency( currencyCode ) {
+	const normalizedCurrencyCode = currencyCode.toUpperCase();
+	switch ( normalizedCurrencyCode ) {
+		case 'AUD':
+		case 'CAD':
+		case 'NZD':
+		case 'USD':
+			return '$';
+
+		default:
+			throw 'Unknown currency symbol';
+	}
+}
+
+/**
+ * Customary decimal and group separators in a given locale.
+ *
+ * @param {string} localeCode ISO 3166-1 alpha-2 region code
+ * @returns {{decimalSeparator:string, groupSeparator:string}} Decimal and group separators
+ */
+function separatorsForLocale( localeCode ) {
+	const normalizedLocaleCode = localeCode.toLowerCase();
+	switch ( normalizedLocaleCode ) {
+		case 'gb': // United Kingdom
+		case 'jp': // Japan
+		case 'nz': // New Zealand
+		case 'us': // United States
+			return { decimalSeparator: '.', groupSeparator: ',' };
+
+		case 'au': // Australia
+			return { decimalSeparator: '.', groupSeparator: ' ' };
+
+		case 'br': // Brazil
+			return { decimalSeparator: ',', groupSeparator: '.' };
+	}
+}