The US Dollar Index (USDX) is an index (or measure) of the value of the United States dollar relative to a basket of foreign currencies.
It is a weighted geometric mean of the dollar's value compared only with
USDX goes up when the US dollar gains "strength" (value) when compared to other currencies.
USDX started in March 1973, soon after the dismantling of the Bretton Woods system. At its start, the value of the US Dollar Index was 100.000. It has since traded as high as 148.1244 in February 1985, and as low as 70.698 on March 16, 2008.
The makeup of the "basket" has been altered only once, when several European currencies were subsumed by the Euro at the start of 1999.
USDX is updated whenever US Dollar markets are open, which is from Sunday evening New York time (early Monday morning Asia time) for 24 hours a day to late Friday afternoon New York time.
USDX can be traded as a futures contract on the IntercontinentalExchange (ICE). It is also available in exchange traded funds (ETFs), options and mutual funds.