Online currency converters typically show a mid-market rate, which is the midpoint between buy and sell prices quoted across major liquidity venues. It’s a useful neutral reference, but it is not the rate you’ll usually get at a bank, payment card, or kiosk.

Where the numbers come from

Aggregators ingest prices from multiple sources (market-makers, FX venues, and reference feeds). Most consumer tools cache results for seconds to a few minutes to balance freshness with stability. That’s why the display rate may update every 1–60 seconds, while your bank rate can lag longer or apply a daily fixing.

Mid-market vs. the rate you pay

Card processors & banks: typically apply their own book or network rate plus a spread.
Money transfer apps: either add a fee, widen the rate, or both; some show fees separately.
Cash exchange counters: wider spread, especially at airports, to cover cash handling.

Update intervals & volatility

During calm markets, rate snapshots may look steady. In high-volatility windows (major data releases, central-bank decisions), prices can move rapidly; converters may throttle updates to avoid flicker, while your provider may widen spreads or temporarily pause quotes.

What to look for when comparing

Compare the all-in cost: displayed rate vs. your provider’s final rate after fees.
Check whether fees are embedded in the rate or shown as a separate line.
Note the timestamp and source of the quote; stale data can mislead.

Bottom line

Use mid-market rates to benchmark, then factor in provider markups and any fixed/percentage fees to estimate the real-world total for your conversion or transfer.