1. Start with a clear pair
Open the website converter. Select EUR in From, USD in To, and enter 10.
Suppose the rate were 1 EUR = 1.20 USD. Your result would be 12 USD. All numbers in this example use an invented rate.
2. Press the swap button
Use the arrow button between the currency fields. On the Lineium website, swapping exchanges the From and To currencies and keeps your input number unchanged.
That means your new question is “What is 10 USD in EUR?” It is not automatically “What is that previous 12 USD result in EUR?”
At our example rate, 10 USD is about 8.33 EUR. A different result after swapping is expected because you changed what the input number represents.
3. Enter the previous result to check the return trip
To reverse the original conversion, keep USD in From and EUR in To, then replace 10 with 12. At the same underlying rate, that takes you back to 10 EUR.
Small differences can appear if you reuse rounded results. A rate refresh between checks can also change the calculation.
4. Read the sentence before the number
Before using any result, say the pair to yourself: “I am converting this many US dollars into euros.” It’s a quick way to catch a reversed pair.
This is especially helpful when you alternate between understanding local prices and checking what your home currency budget represents abroad.
The swap steps above describe the website’s current controls. For more on reversing the arithmetic, see how to calculate an exchange rate. Or try a swap yourself.
Written by Lineium, publisher of Worldwide Currency Converter. App features: Google Play listing. Examples use fictional rates unless stated otherwise.