Bill customers in their own currency

Fetch every rate you sell in, once

Ask for all your currencies in a single call rather than one call per customer. A daily job over nine currencies is one request, not nine.

curl "https://api.currency-rate-api.com/api/v1/rates/latest?base=USD&symbols=EUR,GBP,JPY,CHF,CAD,SEK,PLN,INR,BRL" \
  -H "Authorization: Bearer YOUR_API_KEY"

Rates update once daily via a scheduled ingestion job, so there is no reason to call this more than once a day per base currency — cache the response for the rest of the day.

Convert, then apply your margin

Convert the base price at the published rate, then apply whatever spread covers your payment costs. Keep the two operations separate so you can change the margin without re-deriving prices.

const mid   = Number(rates.EUR);
const gross = basePriceUsd * mid;
const price = gross * (1 + marginPct / 100);

// 49.00 × 0.921000 × 1.015 = 45.82 EUR

Round at the very end. Our API always returns amounts to two decimal places — for a currency with no minor unit, like JPY, you still need to round to a whole unit yourself before charging.

Lock the rate on the subscription

Write the rate and its timestamp onto the subscription at signup, in your own database. The customer then sees a stable price, and a rate move mid-cycle does not surprise anyone.

await db.subscriptions.update(id, {
  billingCurrency: 'EUR',
  lockedRate: '0.921000',
  lockedAt: '2026-08-06T00:00:00Z',
  lockExpiresAt: addDays(now, 90),
});

Ninety days is a common window. Shorter and customers notice churn in their bill; longer and you carry the currency risk.

Reproduce any past invoice

When a customer disputes a charge from March, fetch the historical rate for that exact date and show the arithmetic. It resolves in one reply instead of an escalation.

curl "https://api.currency-rate-api.com/api/v1/rates/2026-03-01?base=USD&symbols=EUR" \
  -H "Authorization: Bearer YOUR_API_KEY"

# { "base": "USD", "date": "2026-03-01", "rates": { "EUR": "0.910700" } }
# 49.00 × 0.910700 × 1.015 = 45.31 EUR