When looking at financial charts like bigcharts.com, the chart shows closing price (or OHLC) for each day. This shows growth (or decline) of the equity if dividends are not reinvested.
But what if dividends are reinvested? How can you chart historical growth/decline taking that into account?
As DStanley stated, some data provider adjust the closing price to reflect dividends and stock splits into account. Stockcharts.com and Yahoo Finance are two that I know of that offer adjusted data. I'm not a fan of Yahoo because their data often has errors.
The adjustment of closing data is important to chartists as well for your situation because with adjusted close data, it's easier to examine historical returns. For me, it's even easier just to plop the numbers into a DRIP calculator that provides a comparison return of reinvesting the dividends(s) versus not reinvesting the dividend(s):
Some providers will include an "adjusted close" that takes dividends (and splits for stock) into account. If that is not available, then you'll probably have to manually adjust the closing prices, either adding dividends to the closing price after it's paid, or reducing closing prices before it's paid.
Ideally, you'd also have to account for the additional return from the dividend (in other words, don't just scale all prices in parallel but make the curve steeper), but the difference may not be significant enough to be worth the extra effort.
