The percent change formula is a basic but useful tool. You can apply it to any variable that’s observed at various points in time. For all variables for which you want to measure the percent change, use the following formula:

Because the subject here is the exchange rate, suppose that X denotes the exchange rate. Also:

• %delta is the percent change.

• Xt is the exchange rate in the current period (t).

• Xt – i is the exchange rate in the previous period (t – i), where i can be yesterday, last month, last year, or ten years ago.

To find the percent change in the exchange rate, start with the current exchange rate minus the previous exchange rate, divide that answer by the previous exchange rate, and then multiply by 100 to express the change as a percent.

The table shows the monthly dollar–euro exchange rates as of the first of every month between January and August 2012.

The Dollar–Euro Monthly Exchange Rate (2012)
Date Exchange Rate Percent Change Terminology (Refers to the Dollar)
January 1.2910
February 1.3238 +2.54 Depreciation
March 1.3208 –0.23 Appreciation
April 1.3160 –0.36 Appreciation
May 1.2806 –2.69 Appreciation
June 1.2541 –2.07 Appreciation
July 1.2278 –2.10 Appreciation
August 1.2406 +1.04 Depreciation