S&P 500 Divisor:

But if you're Dow Jones, you decide that you don't like either of those options. Less than a month later, it dropped to 1,, and would not see similar levels again for five years. The present divisor, after many adjustments, is less than one meaning the index is larger than the sum of the prices of the components.

S&P 500 Divisor Historical Data

These actions do not affect the value of a stock in a market-cap-weighted index. The issuance of additional stock by a company is a corporate action that affects the value and divisor of a market-cap-weighted index.

Each time one of these corporate actions is initiated by a component company, the divisor will be adjusted to keep the index relevant to stock market values. Tim Plaehn has been writing financial, investment and trading articles and blogs since His work has appeared online at Seeking Alpha, Marketwatch. Plaehn has a bachelor's degree in mathematics from the U. At the center of everything we do is a strong commitment to independent research and sharing its profitable discoveries with investors.

This dedication to giving investors a trading advantage led to the creation of our proven Zacks Rank stock-rating system. These returns cover a period from and were examined and attested by Baker Tilly, an independent accounting firm. Visit performance for information about the performance numbers displayed above. Skip to main content. Establishing an Index A company setting up a new stock market index uses a divisor in the initial formation of the index to set up the start value for the index.

Types of Stock Indexes Most stock indexes can be classified as one of two types. Changing Index Components The divisor for a stock index will change when the index drops and adds component stocks. Corporate Actions Actions by the component stocks and companies affect the divisor of an index. Video of the Day. About the Author Tim Plaehn has been writing financial, investment and trading articles and blogs since Zacks Research is Reported On: This allows you to have a superficially simpler index, in that all you have to do is look at stock prices.

Any time any stock price increases by a dollar, your index increases by half a point. Why half a point? Because you have two stocks. If you had 10 stocks, you would divide by Now, I said this is superficially simpler. That's because if one of the stocks goes up by a dollar, the index goes up half a point, regardless of which stock is went up. But if the capitalization on one company goes up by a dollar, the change in index depends on which stock went up.

A further issue is how to handle splits. So if you do an average of the stock prices, it will be The index dropped points, just because one of the companies decided to do a stock split.

If you don't want your index dropping every time a stock splits, you need to do something about that. If you were smart, you'd realize this "look at stock price" thing, although initially simpler, is really not a good idea, and switch to market capitalization. If you were insistent on continuing your current index, you could adjust all the current stock prices and find their pre-split equivalents; since XYZ has a current split factor of 2, you could multiply their stock price by 2, add that to ABC, take the average, and then you would have the same index as before the split.

But if you're Dow Jones, you decide that you don't like either of those options. Instead of adjusting individual stocks, you'll adjust the index as a whole. The index went down by a factor of 0. It's calculated by taking the sum of the new prices, multiplying by the previous divisor, and then dividing the the sum of old prices.

Every time a stock splits, this Dow Divisor has to be recalculated. Using this metehod means that the although the value of the index doesn't change at a stock split, its relationship to stock price does. Every time a stock splits, its effect on the DJIA decreases. There are also adjustments to the DJIA whenever a company buys another one, but the details depend on whether both companies were originally in the DJIA, or just the buyer was, or just the bought company was, and it also depends on how the deal is structured.

If a company in the DJIA splits into two companies, that can also require an adjustment. The index divisor is a number arbitrarily chosen on day 1 and subsequently adjusted when necessary to make the index point continuous. Therefore it by nature is a recursively defined numerical series. To calculate the current divisor, you either need to calculate from previous value, or - if you don't know the previous value - from the previous value of previous value recursive, right?

To calculate the current divisor from scratch, you will need to go all the way back to the day DJIA was introduced, when the initial divisor was chosen , instead of calculated, and apply all the historical adjustments up to date. On the very first day of DJIA May 26, , the initial divisor was arbitrarily chosen to scale the calculated index value to a number that is easy to work with.

Given DJIA is a price weighted index, and its day-1 point was Well that is just the starting point, you will need to figure out every event in history that impacts the divisor, and apply the methodology of that time to adjust the divisor. This is why in all the systems I worked on as a software developer in financial institutions , a reference divisor, usually T-1 divisor, always needs to be provided by data vendors who track these numbers and changes. Then we apply the methodology others mentioned to calculate the T divisor intraday.

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How is the Dow divisor calculated? Dave Dave 1 2. THat answer also contains vague language, like " based on splits and composition changes". My quesiton is, if the divisor is "0.

Dave, the divisor evolves over time and is calculated on an incremental basis based on "splits and composition changes. That's why the answers don't simply show you how to calculate the divisor in a literal way. In these cases, in order to avoid discontinuity in the index, the Dow Divisor is updated so that the quotations right before and after the event coincide: Plugging the numbers into the above equation, we can determine the new Dow Divisor: Maybe I failed to understand something on Wikipedia but where in that article does it list the formula for coming up with the number like "0.

Also I don't know if the rules of stackoverflow apply to money. Also after reading the PDF in its entirety, I don't see anywhere in there that explains the formula for calculating the divisor.

I thought it was on page 7 but it is not. What page discusses the formula for calculating the divisor? The formula is in the portion that I quoted. If you have an equation with 4 variables and 3 of them are known, it shouldn't be too hard to solve for the 4th.

As others have pointed out, the index and the factor evolve over time, which is why you won't find a closed formula to calculate the factor as of a given date. I inserted the link to the original source for your information.

I am trying to come up with a simple stock example of how a divisor comes to be, and how it changes. Dave There is no formula for calculating the value from scratch. Instead, every time there is stock-split or change in composition, the new value is calculated from the current value using the formula 0xFEE1DEAD quotes e.