Does an Executed Limit Order Imply a Spot Price?
Think of all the limit orders waiting in line, first organized by price, and then by the time the order was placed (earlier orders are closer to the front of the line).  In order for your buy order to trade, there must be no other limit orders of 10.01 or higher, or the sellers order would have matched with them instead. So once your order is filled, the price is 10.00, even if just for a millisecond, because there was a trade at 10.00, even though the price might go right back up after the trade. I can't say I know everything about the underlying details, but from what I understand, your limit buy adds to the bid side of open orders, and one possibility is that someone placed a market order to sell when the bid price for the stock fell to $10 which was matched to your open limit order. So using your terminology, I would say the spot bid price is what fell to $10, even if for a brief moment. Whether or not it is possible for your order to be filled when the limit buy price is deeper than the current bid price is beyond me. It may have something to do with lot sizes.
"You said your strategy was to put it into a index fund.  But then you asked about setting  stock limits.   I'm confused. Funds usually trade at their price at the end of the day, so you shouldn't try to time this at all. Just place your order. If you are buying ETFs, there is going to be so much volume on the market that your small trade is going to have no impact on the price. You should just place a market order. A market order is an order to buy or   sell a stock at the current market   price. A limit order is an order to buy or   sell a security at a specific price. In the US, when you place a trade with any broker, you can either place a limit order or a market order.  A market order just fills your order with the next best sellers in line.  If you place an order for 100 shares, the sellers willing to sell 100 shares at the lowest price will be matched with your order (sometimes you may get 50 shares at one price and 50 shares at a slightly different price).    If your stock has a lot of volatility and you place a market order for a small amount of shares,  you will get the best price. If you place a limit order, you specify the price at which you want to buy shares.  Your order will then only be filled with sellers willing to sell at that price or lower (i.e. they must be at least as good as you specified).  This means you could place an order at a limit that does not get filled (the stock could move in a direction away from your limit price).  If you really want to own the stock, you shouldn't use a limit order.  You shouldn't only use a limit order if you want to tell your broker ""I will only buy this stock at this price or better.""  p.s. Every day that passes is NOT a waste.  It's just a day that you've decided investing in cash is safer than investing in the market." "I can think of the following situations in which one could see a trade occur between the visible best bid & offer: 1) on a public exchange, people have posted hidden limit orders with either bid prices above the best visible bid or offers below the best visible offer, and incoming orders have executed against this hidden liquidity[1]; 2) some orders may have been matched in dark pools which offer ""mid-point matching"" where buy and sell orders are matched using the mid-point of the best available publicly posted bid and offer as the reference price, and which executed trades are then reported to the public markets; or 3) some internalising broker has traded off exchange directly with a client and is now reporting the trade to the public as is often required. Now how exactly any of the above situations indicates that a ""trend is about to come to an end"", I do not know. [1] Exchanges often match orders on a price/visibility/time basis, whereby the orders are prioritised by price (better prices get to trade first), then by visibility (visible orders get to trade first) then by time (first come, first serve)." The opening price is derived from new information received. It reflects the current state of the market. Opening Price Deviation (from Investopedia): Investor expectation can be changed by corporate announcements or   other events that make the news. Corporations typically make   news-worthy announcements that may have an effect on the stock price   after the market closes. Large-scale natural disasters or man-made   disasters such as wars or terrorist attacks that take place in the   afterhours may have similar effects on stock prices. When this   happens, some investors may attempt to either buy or sell securities   during the afterhours. Not all orders are executed during after-hours trading. The lack of   liquidity and the resulting wide spreads make market orders   unattractive to traders in after-hours trading. This results in a   large amount of limit or stop orders being placed at a price that is   different from the prior day’s closing price. Consequently, when the   market opens the next day, a substantial disparity in supply and   demand causes the open to veer away from the prior day’s close in the   direction that corresponds to the effect of the announcement, news or   event. Fair value can mean many different things depending on the context. And it has nothing to do with the price at which your market order would be executed. For example if you buy market, you could get executed below 101 if there are hidden orders, at 101 if that sell order is large enough and it is still there when your order reaches the market, or at a higher price otherwise. "A market sell order will be filled at the highest current ""bid"" price. For a reasonably liquid stock, there will be several buy orders in line, and the highest bid must be filled first, so there should a very short time between when you place the order and when it is filled.   What could happen is what's called front running. That's when the broker places their own order in front of yours to fulfill the current bid, selling their own stock at the slightly higher price, causing your sale to be filled at a lower price.  This is not only unethical but illegal as well. It is not something you should be concerned about with a large broker.   You should only place a market order when you don't care about minute differences between the current ask and your execution price, but want to guarantee order execution. If you absolutely have to sell at a minimum price, then a limit order is more appropriate, but you run the risk that your limit will not be reached and your order will not be filled. So the risk is a tradeoff between a guaranteed price and a guaranteed execution." Rule 610 (Google for it) stands that if Bid and Ask are the same, the market is considered Locked, and the exchange must stop all trading. So the same person can't quote the same bid and ask price. However, HFTs have found ways to circumvent this limitation when exchanges created special order types for them, e.g. Spam-and-Cancel "You can place the orders like you suggested.  This would be useful in a market that is moving quickly where you want to be reasonably sure of execution but don't want the full exposure of a market order.  This won't jump your spot in the queue though in the sense that you won't get ahead of other orders that are ""ready"" for execution just because you have crossed the spread aggressively." It will depend largely on your broker what type of stop and trailing stop orders they provide. Saying that, I have not come across any brokers yet that offer limit orders with trailing stop orders.  Unlike a standard stop order where you can either make it a market stop order or a limit stop order, usually most brokers have trailing stop orders as market orders only, where you can either set the trailing stop to be a dollar value or percentage from the most recent high. Remember also, that trailing stop orders will be based on the intra-day highs and not the highest closing price. That means that if the share price spikes up during the day your trailing stop will move up, and if the price then spikes down you may be stopped out prematurely, after which the price might rally again. For this reason I try to base my trailing stops on the highest closing price by using standard stop loss orders and moving it up manually after the close of trade if the share price has closed at a new high. This takes a few minutes each evening (depending on how many stocks you have to check and adjust the stops for) but gives you more control. Using this method will also enable you to set limit orders attached to your stop loss triggers, and you won't have to keep your trailing too close to the last high price thus potentially causing you to get stopped out prematurely. Slightly off track but may be handy if you set profit targets, my broker has recently introduced Trailing Take Profit Orders. The way it works is, say you have a profit target of 50%, so you buy at $2 and want to take profits if the price reaches $3, you could set your Trailing Take Profit Trigger at say $3.10 or above and set a Trail by Amount of say $0.10. So if the price after hitting $3.10 falls to $3.00 you will be stopped out and collect your profits. If the price moves up to $3.30 and then falls to $3.20, you will be stopped out at $3.20 and make some extra profits. If the price continues going up the Trailing Take Profit will continue to move up always $0.10 below the highest price reached. I think this would be a very useful order if you were range trading where you could set the Trailing Take Profit trigger near recent resistance so you can get out if prices start reversing at or around the resistance, but continue profiting if the price breaks through the resistance.