Free Currency Converter Online — Live ECB Rates, 30+ Currencies, Works Offline

Converting currencies sounds simple — until you need to know which rate to trust, whether your bank is charging a fair margin, or why a tool still works when you're offline at 30,000 feet. Here's how ECB exchange rates work, how the converter is built, and which 32 currencies it supports.

Where the Rates Come From — The ECB

The exchange rates in this tool come from the European Central Bank (ECB), fetched via the Frankfurter API. The ECB publishes reference exchange rates once per business day, usually around 16:00 CET. These are the mid-market rates — the midpoint between buy and sell prices on the interbank market.

Why ECB rates?

• Free — no API key, no account, no rate limits
• Trustworthy — same rates used by Bloomberg, Reuters, and central banks worldwide
• Consistent — published once per day, not subject to real-time speculative swings
• Open data — public domain, no terms of service restrictions on use

The mid-market rate is the fairest reference rate. When your bank gives you a worse rate, the difference is their margin — typically 1–4% for retail customers, up to 8% at airport kiosks.

How the 12-Hour Cache Works

Fetching rates on every page load would hit the API unnecessarily and waste bandwidth. The converter uses a localStorage cache with a 12-hour TTL:

const CACHE_KEY = "cc-rates-v1";
const CACHE_TTL = 12 * 60 * 60 * 1000; // 12 hours in ms

async function fetchRates() {
  // Check cache first
  const raw = localStorage.getItem(CACHE_KEY);
  if (raw) {
    const { rates, fetchedAt } = JSON.parse(raw);
    if (Date.now() - fetchedAt < CACHE_TTL) {
      return rates; // Use cached — no API call
    }
  }

  // Cache stale or missing — fetch fresh
  const res = await fetch("https://api.frankfurter.dev/v1/latest?from=USD");
  const data = await res.json();
  const freshRates = { USD: 1, AED: 3.6725, ...data.rates };

  localStorage.setItem(CACHE_KEY, JSON.stringify({
    rates: freshRates,
    fetchedAt: Date.now(),
  }));

  return freshRates;
}

Result: 1 API call per browser per 12 hours, regardless of how many conversions the user does. The ECB only updates once per day anyway, so a 12-hour window gives you the fresh rate within half a day of ECB publishing it.

Why AED Is Hardcoded

The UAE Dirham (AED) is officially pegged to the US Dollar at a fixed rate of 3.6725 AED = 1 USD by the UAE Central Bank. This rate has been fixed since 1997 and does not fluctuate. The ECB doesn't publish AED data because a pegged currency has no meaningful mid-market rate — it's always 3.6725.

So rather than fetch it (it doesn't exist in ECB data) or omit it (AED is heavily used in business), it's hardcoded:

const freshRates = { USD: 1, AED: 3.6725, ...data.rates };

Offline Fallback Rates

If the API is unreachable (no internet, API outage), the tool falls back to a hardcoded set of approximate rates:

const FALLBACK_RATES = {
  USD: 1, EUR: 0.92, GBP: 0.79, CAD: 1.36, AUD: 1.53,
  INR: 83.5, JPY: 149.5, CHF: 0.90, SGD: 1.34, AED: 3.6725,
  // ... 22 more currencies
};

These are "last known good" approximations — accurate enough for rough estimates but not for financial transactions. The UI shows "Approximate rates — API unavailable" when falling back, so users know the rates aren't live.

All 32 Supported Currencies

*AED pegged to USD at 3.6725 — hardcoded, not fetched from ECB.

Conversion Formula

All ECB rates are expressed relative to USD (base = 1 USD). The conversion between any two currencies is:

result = amount × (toRate / fromRate)

Example: Convert 100 EUR to GBP

• EUR rate (relative to USD): 0.92 (1 USD = 0.92 EUR, so 1 EUR = 1/0.92 USD)
• GBP rate (relative to USD): 0.79

result = 100 × (0.79 / 0.92) = 85.87 GBP

No separate EUR→GBP rate needed — all conversions go through USD as the common base.

When to Use It

Before sending an invoice in a foreign currency — confirm the rate before quoting a price in GBP, EUR, or CAD. Then use the Invoice Generator to create the invoice with the right currency.

For travel budget planning — convert your home currency to the destination currency before you go. The offline cache means it works on the plane too.

For international online shopping — a product listed in USD on a US site might be cheaper (or more expensive) than the equivalent in EUR on a European site once you account for the exchange rate.

For freelancers billing internationally — know what 1,000 USD means in your local currency before accepting a project rate.

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Convert between 32 currencies using live ECB rates — free, no signup, works offline: Currency Converter