There should be few surprises today as the Irish Stock Exchange (ISE) introduces a new methodology for calculating the weighting of stocks.
Under the new rules, only shares available for actual trading will be counted when working out the weighting of each stock in the Iseq indices.
Shares held by interested parties and long-term shareholdings will be excluded, bringing the Iseq in line with international practices.
Smurfit Kappa and Aer Lingus are among the stocks that will see their weightings fall, while financial stocks and CRH will enjoy higher weightings.
The move, which was flagged six months ago, will not result in share-price volatility, said Brian Healy, director of trading and regulation of the ISE.
"If there is volatility, it is likely to come from another blip in bond yields in the US or something expected in China," he said.
The third Friday of every month tends to be a busy day for other indices, leading to a knock-on effect on the Irish market the following Monday.
Almost all institutions with index-tracking funds are expected to have changed the make-up of their funds before today.
Dealers last week attributed falls in the share prices of Blackrock and Glanbia to anticipation of the new weightings.
