When the Japanese Nikkei gained 7.2% during January and the NASDAQ gained 4.1%, you are mistaken when you think that the Nikkei would have made you more money. Yes, you are reading this right. In this case 7.2% is not more but less than 4.1%. I will explain.

To be able to see how 7.2% can be less than 4.1%, you have to take into account the currency that the stock market index is nominated in. The value of the NASDAQ is measured in U.S. Dollars. The value of the Japanese Nikkei index is measured in Japanese Yen.

Thus during January, the NASDAQ gained 4.1% measured in U.S. Dollars. And the Nikkei gained 7.2% measured in Japanese Yen.