Logically and theoretically, the last price traded on any given day should be the same as the closing price of a stock. But that isn't always the case.

In particular, a late-afternoon online search for the closing price or last quote on any stock might reveal conflicting results from different sources.

The Final Half-Hour

In fact, the last trade you see at the moment of the close may not truly be the last trade. Many stocks trade heavily in the last half hour of the trading day. A few minutes are required to process the orders and determine which among them actually was the last trade.

Depending on the exchange or the stock quote service you're using, the genuine last trade may be posted anywhere from 30 seconds to 30 minutes after the closing bell rings.

The Consolidated Quote

To make matters more perplexing, the closing price you see when you search for a quote online is often a consolidated quote. This quote is delivered via a system that pulls transactions from all of the stock exchanges and puts them into one data stream.

In addition to a consolidated closing quote, many exchanges, including the New York Stock Exchange (NYSE) and the Nasdaq, offer an official last trade or closing price for trades on their exchanges.

Hence, you can get what appear to be conflicting last and closing prices.

Assuming you can wait 10 minutes after the close, you'll get a closing price and a last trading price that are identical or close to it.

Except, of course, when after-hours trading comes into play.

After-Hours Impact

Since the advent of after-hours trading in 1991, it has been quite normal to see a last price quote that differs greatly from the closing price of the same stock.

This is because the last price in this instance represents the last transaction that occurred in after-hours trading.

In another instant, the stock may trade again and have a new last price, which may or may not match when compared to the closing price from normal trading hours.