Is it possible to improve stock purchase with limit orders accounting for volatility?
If you can afford the cost and risk of 100 shares of stock, then just sell a put option.  If you can only afford a few shares, you can still use the information the options market is trying to give you -- see below. A standing limit order to buy a stock is essentially a synthetic short put option position. [1]  So deciding on a stock limit order price is the same as valuing an option on that stock. Options (and standing limit orders) are hard to value, and the generally accepted math for doing so -- the Black-Scholes-Merton framework -- is also generally accepted to be wrong, because of black swans. So rather than calculate a stock buy limit price yourself, it's simpler to just sell a put at the put's own midpoint price, accepting the market's best estimate. Options market makers' whole job (and the purpose of the open market) is price discovery, so it's easier to let them fight it out over what price options should really be trading at. The result of that fight is valuable information -- use it. Sell a 1-month ATM put option every month until you get exercised, after which time you'll own 100 shares of stock, purchased at: This will typically give you a much better cost basis (several dollars better) versus buying the stock at spot, and it offloads the valuation math onto the options market.  Meanwhile you get to keep the cash from the options premiums as well. Disclaimer: Markets do make mistakes.  You will lose money when the stock drops more than the option market's own estimate. If you can't afford 100 shares, or for some reason still want to be in the business of creating synthetic options from pure stock limit orders, then you could maybe play around with setting your stock purchase bid price to (approximately): See your statistics book for how to set ndev -- 1 standard deviation gives you a 30% chance of a fill, 2 gives you a 5% chance, etc. Disclaimer: The above math probably has mistakes; do your own work.  It's somewhat invalid anyway, because stock prices don't follow a normal curve, so standard deviations don't really mean a whole lot.  This is where market makers earn their keep (or not). If you still want to create synthetic options using stock limit orders, you might be able to get the options market to do more of the math for you. Try setting your stock limit order bid equal to something like this: Where put_strike is the strike price of a put option for the equity you're trading.  Which option expiration and strike you use for put_strike depends on your desired time horizon and desired fill probability.  To get probability, you can look at the delta for a given option.  The relationship between option delta and equity limit order probability of fill is approximately: Disclaimer: There may be math errors here.  Again, do your own work. Also, while this method assumes option markets provide good estimates, see above disclaimer about the markets making mistakes. There is no such thing as buying at the best price. That only exists in hindsight. If you could consistently predict the lower bound, then you would have no reason to waste your time investing. Quit your job and bet with all leverage in. What if the price never reaches your lower bound and the market keeps rallying? What if today is crash day and you catch a falling knife? I'd say the best strategy would be just buy at whatever the market price is the moment your investment money hits your account with the smallest possible commission. The simplest solution to fire-and-forget is to pick something like a Target Date mutual fund made up of low-overhead index funds (within your 401k or a Roth IRA, perhaps) and set up automatic purchase to that.  If you're talking about limit orders and so on, that ain't simple.
"My answer isn't a full one, but that's because I think the answer depends on, at minimum, the country your broker is in, the type of order you place (limit, market, algo, etc.,) and the size of your order. For example, I can tell from watching live rates on regular lot limit orders I place with my UK-based broker that they hold limit orders internally until they see a crossing rate on the exchange my requested stock is trading on, then they submit a limit order to that exchange.  I only get filled from that one exchange and this happens noticeably after I see my limit price print, and my fills are always better than my limit price. Whereas with my US-based broker, I can see my regular lotsize limit order in the order book (depth of book data) prior to any fills.  I will routinely be notified of a fill before I see the limit price print.  And my fills come from any number of US exchanges (NYSE, ARCA, BATS, etc.) even for the same stock. I should point out that the ""NBBO"" rule in the US, under SEC regulation NMS, probably causes more complications in handling of market and limit orders than you're likely to find in most countries." "There are ways to mitigate, but since you're not protected by a tax-deferred/advantaged account, the realized income will be taxed. But you can do any of the followings to reduce the burden: Prefer selling either short positions that are at loss or long positions that are at gain. Do not invest in stocks, but rather in index funds that do the rebalancing for you without (significant) tax impact on you. If you are rebalancing portfolio that includes assets that are not stocks (real-estate, mainly) consider performing 1031 exchanges instead of plain sale and re-purchase. Maximize your IRA contributions, even if non-deductible, and convert them to Roth IRA. Hold your more volatile investments and individual stocks there - you will not be taxed when rebalancing. Maximize your 401K, HSA, SEP-IRA and any other tax-advantaged account you may be eligible for. On some accounts you'll pay taxes when withdrawing, on others - you won't. For example - Roth IRA/401k accounts are not taxed at all when withdrawing qualified distributions, while traditional IRA/401k are taxed as ordinary income. During the ""low income"" years, consider converting portions of traditional accounts to Roth." I have done this, and the reason is to make sure that I don't run out of money in my account to place the order if there is an unexpected upswing in price. Suppose I have $1000 in my account and I want to buy 10 shares of ABCD that are currently at $99.  If the price doesn't change, then I am all set, but if the price goes up to $101 then I don't have sufficient funds to make the purchase. By placing a limit order at $100 I can ensure that I have enough money to place the order. In general, it is a rather unlikely scenario that it could happen, but placing the limit order is easy to do and it gives me peace of mind. I don't know what you mean about bypassing the queue. I agree that high volatility just means the underlying stock price fluctuates more, and it does not imply if the stock is going up or down. But a high volatility in the price of an underlying also means that there is a higher chance that the underlying price could reach extreme prices (albeit in either direction). However, if you purchased a call option then if the underlying price reached an extremely high value, then you will be richly rewarded. But if the underlying price reached an extremely low value, you won't lose any more than the initial premium that you paid. There is no additional risk on your side, it's capped to the premium that you paid for the call option. It's this asymmetric outcome (Heads - I win, Tails - I don't lose) combined with high volatility that means that call options will increase in value when the underlying price becomes more volatile. If the optionality wasn't there then the price wouldn't be related to the volatility of the underlying. But that would be called a Future or a Forward :-) 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. if you know when and by how much something will fluctuate, you can always make money. Buy it when it's cheaper and sell it when it's more expensive. If you just know that it fluctuated a lot recently, then you don't know what it will do next. Most securities that go to zero or go much higher bounce all over the place for a while first.  But you don't know when they'll move decisively lower or higher.  So how could you figure out if you'll make money - you can't know. DCA will on average make you better off, unless the extra commissions are too high relative to your purchase sizes. But it will in retrospect make you worse off in many particular cases. This is true of many investment disciplines, such as rebalancing. They are all based on averages.  If the volatility is random then on average you can buy more shares when the price is lower using DCA. But when the lowest price turns out to have been on a certain day, you'd have been better off with a single lump sum put in on that day. No way to know in advance.  Degree of volatility shouldn't matter; any fluctuation is enough for DCA or rebalancing to get you ahead, though it's true they get you ahead farther if the fluctuations are larger, since there's then more difference between DCA and a lump purchase.  I think the real reason to do DCA and rebalancing is risk control. They reduce the risk of putting a whole lump sum in on exactly the wrong day. And they can help keep a portfolio growing even if the market is stagnant. There are a couple of things you could do, but it may depend partly on the type of orders your broker has available to you. Firstly, if you are putting your limit order the night before after close of market at the top of the bids, you may be risking missing out if bid & offer prices increase by the time the market opens the next day. On the other hand, if bid & offer prices fall at the open of the next day you should get your order filled at or below your limit price. Secondly, you could be available at the market open to see if prices are going up or down and then work out the price you want to buy at then and work out the quantity you can buy at that price. I personally don't like this method because you usually get too emotional, start chasing the market if prices start rising, or start regretting buying at a price and prices fall straight afterwards. My preferred method is this third option. If your broker provides stop orders you can use these to both get into and out of the market. How they work when trying to get into the market is that once you have done your analysis and picked a price that you would want to purchase at, you put a stop buy order in. For example, the price closed at $9.90 the previous day and there has been resistance at $10.00, so you would put a stop buy trigger if the price goes over $10, say $10.01. If your stop buy order gets triggered you can have either a buy market order or a limit order above $10.01 (say $10.02). The market order would go through immediately whilst the limit order would only go through if the price continues going to $10.02 or above. The advantage of this is that you don't get emotional trying to buy your securities whilst sitting in front of the screen, you do your analysis and set your prices whilst the market is closed, you only buy when the security is rising (not falling). As your aim is to be in long term you shouldn't be concerned about buying a little bit higher than the previous days close. On the other hand if you try and buy when the price is falling you don't know when it will stop falling. It is better to buy when the price shows signs of rising rather than falling (always follow the trend). "Using the following equations from the book a stab at the correlation can be made.   Calculating the residual volatilities from equation 2.4 The correlation of stock A with stock B is 0.378 and stock B has the higher residual volatility. However, the correlation is given as a ""simple model"", which may suggest that it is an approximation.  If I have applied it correctly, some testing shows that it is only approximate. Also of interest"