If a company has undergone stock splits over its lifetime, comparing historical stock prices to those of the present day would not accurately reflect performance. For this reason, we must compare splitadjusted share prices.
The necessity of this adjusted price is best illustrated with an example. We'll use a fictional company, the TSJ Sports Conglomerate. Over the decades, this sports management company has grown a great deal and undergone numerous stock splits. When the company went public in 1988, its shares traded for $10. After some years, the company's share price appreciated to $50, and at that point the management felt that a 2for1 share split was appropriate, thus reducing the cost of a single share to $25. As time went on, the company continued to see a rising share price and, in accordance with the management's policy, the stock was split each time it reached $50. In total, the company split its shares four times since going public. Today, just after its last split, a single share of TSJ is trading at $25.
Because of all these splits, it is easy to see that the share price has appreciated much more than 2.5 times, from $10 to $25. In actuality, because TSJ has undergone four 2for1 splits, one original share in TSJ would be worth approximately $400 today!
No. of Shares  Share Price  Total Value  
1  $ 10  $10  
Split 1  2  $ 25  $50 
Split 2  4  $ 25  $100 
Split 3  8  $ 25  $200 
Split 4  16  $ 25  $400 
Figure 1 
Figure 1 demonstrates how we reach the $400 value. If you bought and held one original share of TSJ until the present day, you would have 16 shares of TSJ (first split: 1x2=2, second split: 2x2=4, third split: 4x2=8, fourth split: 8x2=16). So, even though one of TSJ's current shares is $25, one original share is worth $400 ($25*16), and therefore appreciated 40 times ($400/$10). The TSJ is a quadruple tenbagger  a very elusive investment indeed.
For discerning and analyzing the real performance of the stock, it is standard to adjust the old prices to reflect the splits. In other words, we have to find the present equivalent of the past prices. To adjust TSJ's original price ($10), we simply divide it by the stock split (2). After four times, we get the splitadjusted price.
After the first split, the original initial public offering (IPO) price of $10 would be divided by two, giving a splitadjusted price of $5.
No. of Shares  Adjusted Price  Total Value  
1  $10  $10  
Split 1  2  $5  $10 
Split 2  4  $2.50  $10 
Split 3  8  $1.25  $10 
Split 4  16  $0.625  $10 
Figure 2 
Figure 2 demonstrates how the original $10 price is adjusted after each split  so, after the fourth split, the original $10 price is equivalent to $0.625 today. If you were to look at a stock chart of TSJ that went back to its initial offering, the first day trading would be shown at $0.625, even though the stock never really traded at this price.
It's important to remember that the split creates no value. Notice how the column on the very right is simply the product of multiplying the number of shares by the splitadjusted price. The gain of 40 times we saw before was the result of growth, not splits.
For more information, see Understanding Stock Splits and What is a stock split? Why do stocks split?
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