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.
"When you place a limit sell order of $10.00 (for a stock on an option) you are adding your order to the book.  Anyone who places a buy at-the-market or with a limit price over $10.00 will have that order immediately fulfilled through the offer you have placed on the book. On the other hand, if that other person places a buy for $8.00, then the spread will now be ""$8.00 bid, $10.00 ask"". Priority is based on first the price (all $9.99 asks will clear before $10.00) and within each bucket this is based on the time your order was submitted. This is why in bidding markets (including eBay) buying at $x.01 is way better than $x.00 and selling at $x.99 is better than $(x+1).00. Source: https://en.wikipedia.org/wiki/Order_(exchange) under ""first-come-first-served""" "One practical application would be to protect yourself from a ""flash crash"" type scenario where a stock suddenly plunges down to a penny due to transient market glitches. If you had a stop-loss order that executed at a penny (for a non-penny stock) it would be probably be voided by the exchange, but you might not want to take that risk." I don't think user4358's explanation is correct.  A trailing LIT Sell Order adjusts downwards, i.e. if you place the order with an Aux price (in TWS it's trigger price) of 105.00 and a trailing amount of 6.00 then, assuming the ask is 100.00, TWS will add the trailing amount to the ask price and if it's less than the trigger price it will adjust. So in my example, if the market (ask) goes straight up to 105.00, nothing will be adjusted, the trigger is touched and the limit order will be placed (see below). If on the the other hand the market goes down to 99.00 then trlng amt + ask is 105.00, if it goes further down to 98.00 then the trigger price will be adjusted to 104.00 (because it's less than the current trigger), and so on. For the LIT part you have either an absolute limit price you can enter, or you have an offset limit which will be subtracted from the trigger price, in which case it is adjusted as well. So back to my example, the trigger is now 104.00 and the limit offset is say 1.00, so my limit order would be placed at 103.00 if the ask ever touches 104.00, and that in turn is only visible if the bid touches 103.00 (because it's limit-if-touched). For a buy just use the same explanation with some swapped roles, the trigger price adjust upwards when the trailing amount plus bid is larger than the current trigger, and the limit offset will be added to the trigger price. Edit Also quite succinct and worth having a look at: http://www.interactivebrokers.com/en/trading/orders/trailingLimitTouched.php Guesswork, highly subjective As for why this might be good, well, you have to believe in momentum strategies, i.e. a market that goes down, will continue to go down, if you believe that and you believe in mean reversion as well, then a trailing limit order can assist you in not buying/selling impulsively, but closer to the mean.  I've never used it that way though. What I have done, even just now to get the explanation right, is to place trailing buy and sell orders simultaneously.  You will find that you can just go in with coarse estimates and because the adjustments will go towards each other, you will end up with a narrowing band of trigger prices (as opposed to trailing stop orders which will give you a widening band of trigger prices).  If you believe in overshooting and equilibria then this can be one easy way to profit from it.  I've just sold EURUSD for 1.26420 and bought it back at 1.26380 with a trailing amount of 5pips and a limit offset of 2pips within the time of writing this. The next day the market opens trading at 10.50, You haven't specified whether you limit order for $10.10 is to buy or sell. When the trading opens next day, it follows the same process of matching the orders. So if you have put a limit order to buy at $10.10 and there is no sell order at that price, your trade will not go through. If you have placed a limit sell order at $10.10 and there is a buyer at or higher price, it would go through. The Open price is the price of the first trade of the day. "In a sense, yes. There's a view in Yahoo Finance that looks like this   For this particular stock, a market order for 3000 shares (not even $4000, this is a reasonably small figure) will move the stock past $1.34, more than a 3% move.  Say, on the Ask side there are 100,000 shares, all with $10 ask. It would take a lot of orders to purchase all these shares, so for a while, the price may stay right at $10, or a bit lower if there are those willing to sell lower.  But, say that side showed $10 1000, $10.25 500, $10.50 1000. Now, the volume is so low that if I decided I wanted shares at any price, my order, a market order will actually drive the market price right up to $10.50 if I buy 2500 shares ""market"".  You see, however, even though I'm a small trader, I drove the price up. But now that the price is $10.50 when I go to sell all 2500 at $10.50, there are no bids to pay that much, so the price the next trade will occur at isn't known yet. There may be bids at $10, with asking (me) at $10.50. No trades will happen until a seller takes the $10 bid or other buyers and sellers come in." "The answer to each of your questions is no. It is important to appreciate that the ""quoted"" ticker price may be delayed by say 15 minutes, and thus is not ""real-time.""" Yes there will be enough liquidity to sell your position barring some sort of Flash Crash anomaly. Volume generally rises on the day of expiration to increase this liquidity. Don't forget that there are many investment strategies--buying to cover a short position is closing out a trade similar to your case. Buy and sell orders always include the price at which you buy/sell. That's how the market prices for stocks are determines. So if you want to place a buy order at 106, you can do that. When that order was fulfilled and you have the stock, you can place a sell order at 107. It will be processed as soon as someone places a buy order at 107. Theoretically you can even place sell orders for stocks you haven't even bought yet. That's called short selling. You do that when you expect a stock to go down in the future. But this is a very risky operation, because when you mispredict the market you might end up owing more money than you invested. No responsible banker will even discuss this with you when you can not prove you know what you are doing. Yes for every order there is a buyer and seller. But overall there are multiple buyers and multiple sellers. So every trade is at a different price and this price is agreed by both buyer and seller. Related question will help you understand this better. How do exchanges match limit orders? Depending on your strategy, it could be though there is also something to be said for what kind of order are you placing: Market, limit or otherwise? Something else to consider is whether or not there is some major news that could cause the stock/ETF to gap at the open.  For example, if a company announces strong earnings then it is possible for the stock to open higher than it did the previous day and so a market order may not to take into account that the stock may jump a bit compared to the previous close.  Limit orders can be useful to put a cap on how much you'll pay for a stock though the key would be to factor this into your strategy of when do you buy. "You can interpret prices in any way you wish, but the commonly quoted ""price"" is the last price traded. If your broker routes those orders, unlikely because they will be considered ""unfair"" and will probably be busted by the exchange, the only way to drive the price to the heights & lows in your example is to have an overwhelming amount of quantity relative to the order book. Your orders will hit the opposing limit orders until your quantity is exhausted, starting from the best price to the worst price. This is the functional equivalent to a market order." This sometimes happens to me. It depends on how liquid the option is. Normally what I see happening is that the order book mutates itself around my order. I interpret this to mean that the order book is primarily market makers. They see a retail investor (me) come in and, since they don't have any interest in this illiquid option, they back off. Some other retail investor (or whatever) steps in with a market order, and we get matched up. I get a fill because I become the market maker for a brief while. On highly liquid options, buy limits at the bid tend to get swallowed because the market makers are working the spread. With very small orders (a contract or two) on very liquid options, I've had luck getting quick fills in the middle of the spread, which I attribute to MM's rebalancing their holdings on the cheap, although sometimes I like to think there's some other anal-retentive like me out there that hates to see such a lopsided book. :) I haven't noticed any particular tendency for this to happen more with puts or calls, or with buy vs sell transactions. For a while I had a suspicion that this was happening with strikes where IV didn't match IV of other strikes, but I never cared enough to chase it down as it was a minor part of my overall P/L. There are people whose strategy revolves around putting orders at the bid and ask and making money off people who cross the spread.  If you put an order in between the current bid/ask, people running that type of strategy will usually pick it off, viewing it as a discount to the orders that they already have on the bid/ask.  Often these people are trading by computer, so your limit order may get hit so quickly that it appears instantaneous to you.  In reality, you were probably hit by a limit order placed specifically to fill against yours. Stop order is triggered when the market reaches the price you set. Until then - its not on the books. Your understanding is wrong in that you don't go to read the definition of the term. Checkout the worksheet on page 20 of Pub 535.  Also the text starting in the last half of the third column of page 18 onward. https://www.irs.gov/pub/irs-pdf/p535.pdf The fact that you get a W-2 is irrelevant as far as I can see.  Your self-employment business has to meet some criteria (such as being profitable) and the plan needs to be provided through your own business (although if you're sole proprietor filing on Schedule C, it looks like having it in your own name does the trick).  Check the publication for all of the rules. There is this exception that would prevent many people with full-time jobs on W-2 from taking the deduction: Other coverage. You cannot take the deduc­tion for any month you were eligible to partici­pate in any employer (including your spouse's) subsidized health plan at any time during that month, even if you did not actually participate. In addition, if you were eligible for any month or part of a month to participate in any subsidized health plan maintained by the employer of ei­ther your dependent or your child who was un­der age 27 at the end of 2014, do not use amounts paid for coverage for that month to fig­ure the deduction. (Pages 20-21).  Sounds like in your case, though, this doesn't apply. (Although your original question doesn't mention a spouse, which might be relevant to the rule if you have one and he/she works.) The publication should help.  If still in doubt, you'll probably need a CPA or other professional to assess your individual situation.