A number of shares will be on watch on Monday after S&P Dow Jones Indices announced its quarterly changes to the S&P/ASX Indices. These are effective prior to the open of trading on 23 September and follow its latest quarterly review.

Here is a summary of some of the key changes being made:

New ASX 200 shares

S&P/ASX Indices have announced three new additions to the ASX 200 index at the quarterly rebalance.

The first is newly listed quick service restaurant operator Guzman Y Gomez Ltd (ASX: GYG). It has taken the company less than two months since listing to gain inclusion to the illustrious index.

Another new addition to the benchmark index is Westgold Resources Ltd (ASX: WGX). It is a West Australian gold producer located in the Murchison and Southern Goldfields regions. The company has tenure of more than 3,200 km2 and operates six underground mines and five processing plants with an installed processing capacity of approximately 6.6 million tonnes per annum.

Last month, it released its full year results and revealed a 9% lift in revenue to $716 million and a 62% increase in EBITDA to $271 million.

A third share that is joining the ASX 200 index later this month is coal miner Yancoal Australia Ltd (ASX: YAL). It recently released its half year results and revealed a 57% decline in profit after tax to $420 million. This was driven by a sharp decline in realised coal prices.

Shares being kicked out

Given that there were already 200 shares included in the index, three need to make way for these new additions.

The unlucky three includes property listings company Domain Holdings Australia Ltd (ASX: DHG). Its shares have lost 28% of their value over the past 12 months.

Also leaving the benchmark index later this month will be medical device company Nanosonics Ltd (ASX: NAN). A poor performance in FY 2024 has weighed heavily on the company's shares. For example, last month it reported a 35% decline in profit after tax to $13 million.

Finally, Strike Energy Ltd (ASX: STX) is being kicked out of the ASX 200 this month. This is unlikely to be a surprise given how much its market capitalisation has dropped over the past 12 months due to disappointing exploration results.

What now?

Given how some fund managers have strict investment mandates that mean they can only buy shares from certain indices, this news is likely to be a boost to the shares being added to indices and the opposite for those removed.

In addition to this, index-tracking ETFs will need to buy and sell these shares in order to accurately reflect the indices.