Provider rate: mid-market, Visa, Mastercard or bank
The exchange rate the card converts at, and which yardstick it uses.
Mid-market (sometimes called the interbank rate) is the midpoint between buying and selling prices, and is broadly the rate you'll see on services like Google. Visa and Mastercard set their own daily rates that sit very close to it. A bank rate is the issuer's own rate, and can be 2 to 4 percent worse before any fee is added.
For consistency, we compare every card using the mid-market rate and apply each card's fees separately. Visa and Mastercard rates change daily and are usually within a fraction of a percent of the mid-market rate, so the difference is typically very small. Each card's rate line in the live calculator names the rate we used.