Data Methodology & Trust

Reference rate vs. transaction rate

A reference rate is a single mid-market figure published by an authority (such as the European Central Bank) or aggregated by an open data provider. It is a snapshot of where a currency pair traded at a specific time and is widely used for accounting, reporting, and informational comparisons.

A transaction rate is the price you actually pay or receive when exchanging money — at a bank, broker, ATM, card network, or money-transfer service. It typically differs from the reference rate by a spread or fee, and changes continuously throughout the day.

Data sources

• Fiat reference rates (161 currencies). Aggregated daily mid-market rates from open.er-api.com. These are published as the latest available reference rate and cover all currencies on the map.
• ECB historical series (31 currencies). Sourced from the Frankfurter API, which mirrors the European Central Bank's daily euro reference rates published around 16:00 CET on TARGET business days. Historical sparkline charts and percentage-change tables use this dataset where available.
• Cryptocurrencies. Top crypto prices (Bitcoin, Ethereum, and other majors) are sourced from CoinGecko. Crypto prices change second-by-second on exchanges; the values shown here are the latest available snapshot at our refresh cadence and are not real-time exchange quotes.
• Precious metals & oil. Spot prices for gold (XAU), silver (XAG), platinum (XPT), palladium (XPD), and crude benchmarks (WTI, Brent) are sourced via open.er-api.com with gold-api.com as a fallback.
• Big Mac Index. Local Big Mac prices come from The Economist’s official open dataset (github.com/TheEconomist/big-mac-data), which is published roughly twice a year. We always show the most recent survey. The Big Mac Index is an informal purchasing-power-parity (PPP) indicator.
• Purchasing-power map. The map’s purchasing-power lens combines World Bank PPP conversion factors for private consumption (PA.NUS.PRVT.PP, CC BY-4.0) with live market exchange rates to estimate a price level per country, normalised against the global median.
• Affordability & fun indexes. The Latte, Taxi, Coca-Cola, Movie Ticket, and Gasoline indexes use approximate average prices derived from Numbeo and other public sources. They are intended for entertainment and rough comparison only — actual prices vary significantly by city, vendor, and season.
• Cost of living. Country-level cost-of-living scores are computed from the affordability indexes above and are normalised against a global median.

Update cadence

fxmap.app does not connect to a real-time trading feed. Data is pulled from upstream sources on the following schedule:

• Fiat & crypto rates: a scheduled cron job refreshes the latest snapshot approximately every hour. The page-level timestamp (“Updated …”) reflects theupstream publication time, not necessarily the wall-clock time of your visit.
• ECB historical series: the ECB publishes rates once per business day (T+1). Weekend and holiday values are forward-filled from the most recent business day.
• Big Mac & affordability indexes: refreshed monthly.

Cache behaviour

To keep the site fast and resilient, rates are served from a tiered cache:

• Each upstream snapshot is persisted to a Supabaserate_snapshotstable with its own recorded_at timestamp.
• The application server holds an in-memory cache with a 1-hour TTL. HTTP responses set s-maxage=3600 with a 2-hour stale-while-revalidate window so the CDN can keep serving during brief upstream outages.
• The last updated value displayed on each page is the asOf timestamp from the underlying snapshot, not the time the cached response was returned. When the site can't reach fresh data, you may see “Showing cached data — rates may be outdated”.

Limitations

• Rates here are indicative reference rates — they will differ from the bid/ask spread you see at a bank or broker.
• Refresh cadence is hourly, not real-time. Markets can move meaningfully between refreshes, especially for volatile emerging-market currencies and crypto.
• Pegged and managed currencies (e.g. HKD, SAR, AED) reflect the official peg rate, which can deviate from offshore or parallel-market rates.
• Some thinly-traded currencies are derived from cross-rates rather than direct quotes.
• Affordability indexes (Latte, Taxi, Coca-Cola, Movie, Gas) use approximate national averages and do not reflect specific vendors, cities, or seasons.
• Historical charts may forward-fill weekends and holidays using the previous business day's ECB rate.