What is currency conversion, and what is DCC?
The fee is hidden inside a number that changes every second, which is precisely the point.
It is being asked, at a foreign railway station, whether you would like to buy your ticket from the official counter or from a helpful man beside it who will happily quote you a price in your own money.
The fee is not a line on the receipt. It is the distance between two numbers, and you agreed to it by pressing a helpful looking button.
The rate that actually exists
Search any currency pair and you get the mid-market rate: the genuine wholesale price at which currencies trade between institutions. That is the real number.
Now look at what your bank, card, or app gave you. It will be worse. Not because of an error, but because that difference is the product. On a 2 percent spread, converting 5 lakh rupees quietly costs 10,000 rupees, and no line item anywhere says so.
This is the single most effective fee design in finance: it is charged inside a number that moves every second anyway, so you cannot easily prove what you lost.
Dynamic currency conversion: the trap with a friendly face
Now the specific thing to watch for. You are abroad, you pay by card, and the terminal asks whether you would like to be charged in your home currency instead of the local one. It looks like a courtesy. It is called dynamic currency conversion, and you should almost always decline.
Choosing your home currency hands the conversion to the merchant's payment provider, who sets the rate and typically applies a markup well above what your own card would have charged. You gave up your bank's rate for a stranger's rate, in exchange for seeing a familiar currency symbol on a receipt you will not check.
Always choose the local currency. Let your own card do the conversion. That single habit is worth more than most travel money advice combined.
Where you meet it
Every international transfer, every foreign card payment, every ATM abroad, and every terminal that offers you the friendly choice. The sixty second check: search the mid-market rate, compare it to what you were offered, multiply the gap by your amount. That is your real fee.