The Advance/Decline Index is a market breadth indicator that represents the cumulative difference between the number of advancing and declining stocks.
The index is constructed by adding the total number of stocks that have advanced for the day to the total number of stocks that have declined and dividing by 2.
The index can be considered as a measure of market breadth, with an increase in this index indicating more participation in the market rally.
The Advance/Decline Index can be calculated on both a daily and weekly basis, but typically only one is reported to avoid confusion between short-term and long-term trends.