Rand isn't world's most undervalued currency any more. It should trade at R6/$, index shows Business Insider SA facebook email The Economist's Big Mac index shows that - theoretically - the rand should be trading at R5.92/dollar. The currency is undervalued by 62% against the dollar, compared to currencies in Brazil (-30%) and India (-54%). But six months ago, it was undervalued by even more – and it was also the world’s most undervalued currency. Now currencies in Russia and Turkey fare worse. For more articles, go to . Since 1986, the publication has been using McDonald’s Big Mac prices to determine whether currencies are overvalued, or too cheap.