Change 100 euros at the airport and get 88 back

You change 100 euros for dollars at the Barajas airport counter. The board says 1.09 dollars per euro. You sign, take 88, and walk away pleased.

The arithmetic they don't spell out: the visible fee is 3 percent, say 3 euros. The other 9 show up nowhere. They are eaten by the "spread", the gap between the counter's buy and sell prices: they change you at 1.00 instead of the real 1.09 the markets had that day. Selling high and buying low is their business; the big sign gives you confidence and the spread empties your pocket.

Compare it with what a neobank card does through its app: a transfer at the interbank rate, a 1 euro fee, and cash out at the arrival airport in two minutes from a neutral ATM. You change 100 and get 108 dollars at the real rate, minus one euro for handling: you end up with the equivalent of 107.

Difference per transaction: 19 dollars. On a week-long trip with 400 euros changed, 76 dollars. Over two trips a year, a 150 note you left on the counter out of habit.

Open your bank's app before you fly. Transfer now, withdraw at arrival: every 100 euros come out as 107 dollars at the destination airport, not 88 at the one you departed from.