Buying under my bid price
It definitely depends on the exchange you are trading on. I'm not familiar with Scottrade, but a standard practice is to fulfill limit orders in the order they are placed.   Most of the time, you wouldn't see stocks trade significantly under your bid price, but since penny stocks are very volatile, it's more likely their price could drop quickly past your bid and then return above it while only fulfilling a portion of the orders placed. Example 1. Penny stock priced at $0.12 2. Others place limit orders to buy at $0.10 3. You place limit order to buy at $0.10 4. Stock price drops to $0.07 and some orders are filled (anything $0.07 or higher) based on a first-come first-served basis 5. Due to the increase in purchases of the penny stock, the price rises above $0.10 before your order is filled ***EDIT*** - Adding additional clarification from comment section. A second example If the price drops from $0.12 to $0.07, then orders for all prices from $0.07 and above will start to be filled from the oldest order first. That might mean that the oldest order was a limit buy order for 100 shares at $0.09, and since that is above the current ask price, it will be filled first. The next order might be for 800 shares at $0.07. It's possible for a subset of these to be filled (let's say 400) before the share's price increases from the increased demand. Then, if the price goes above $0.10, your bid will not be filled during that time.
"ETFs are well suited to day trading, but you should be mindful of the bid-ask spread. See article: Commission-free ETFs are a great way to save money, but watch the bid-ask spread too. Bid-ask spread is largely a function of liquidity, or the volume of   buyers and sellers for an asset during a particular moment in time.   ... It may be more difficult to trade certain assets that are less   liquid, where bid-ask spreads can be higher. Think some penny stocks. If you have the choice, compare the spreads of the ETF and the target stock. Longer-term ""keep & hold"" trading on ETFs tracking futures can be somewhat disadvantageous.  Futures contracts roll-over every month.  Exchange traders have to sell and buy in on the next contract.  ETFs don't reflect the price differential between the futures contract. See here for more detail on that: Positioning For An Oil ETF Rebound? Watch For Contango Contango occurs when the price on a futures contract is higher than   the expected future spot price, which creates the upward sloping curve   on future commodity prices over time. Essentially, the phenomenon   reflects a current spot price that is lower than the futures price.   ... While this phenomena is a normal occurrence in the futures market,   contango can have a negative effect on ETFs." "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." Market price simply depends on your order side.  If you are placing a buy order the market price is the lowest ask, if you are placing a sell order the market price is the highest bid.  If your order is larger than the volume then you'd need to also consider the next lowest ask or next highest bid until you've fulfilled your order volume. "Well, futures don't have a ""strike"" like an option - the price represents how much you're obligated to buy/sell the index for at a specified date in the future.  You are correct that there's no cost to enter a contract (though there may be broker fees and margin payments).  Any difference between the contract price and the price of the index at settlement is what is exchanged at settlement.   It's analogous to the bid/ask on a stock - the bid price represents the price at which someone is willing to ""buy"" a futures contract (meaning enter into a long position) and the ask is how much someone is willing to ""sell"" a contract. So if you want to take a long position on S&P500 mini futures you'd have to enter in at the ""ask"" price.  If the index is above your contract price on the future expiry date you'll make a profit; if it is below the contract price you'll take a loss." As you mentioned in the title, what you're asking about comes down to volatility.  DCA when purchasing stock is one way of dealing with volatility, but it's only profitable if the financial instrument can be sold higher than your sunk costs.  Issues to be concerned with: Let's suppose you're buying a stock listed on the NYSE called FOO (this is a completely fake example).  Over the last six days, the average value of this stock was exactly $1.00Note 1.  Over six trading days you put $100 per day into this stockNote 2: At market close on January 11th, you have 616 shares of FOO.  You paid $596.29 for it, so your average cost (before fees) is: $596.29 / 616 = $0.97 per share Let's look at this including your trading fees: ($596.29 + $30) / 616 = $1.01 per share. When the market opens on January 12th, the quote on FOO could be anything.  Patents, customer wins, wars, politics, lawsuits, press coverage, etc... could cause the value of FOO to fluctuate.  So, let's just roll with the assumption that past performance is consistent: Selling FOO at $0.80 nets: (616 * $0.80 - $5) - ($596.29 + $30) =  $123.49 Loss Selling FOO at $1.20 nets: (616 * $1.20 - $5) - ($596.29 + $30) =  $107.90 Profit Every day that you keep trading FOO, those numbers get bigger (assuming FOO is a constant value).  Also remember, even if FOO never changes its average value and volatility, your recoverable profits shrink with each transaction because you pay $5 in fees for every one. Speaking from experience, it is very easy to paper trade.  It is a lot harder when you're looking at the ticker all day when FOO has been $0.80 - $0.90 for the past four days (and you're $300 under water on a $1000 portfolio).  Now your mind starts playing nasty games with you. If you decide to try this, let me give you some free advice: Unless you have some research (such as support / resistance information) or data on why FOO is a good buy at this price, let's be honest: you're gambling with DCA, not trading. END NOTES: Oh really. I will have to check into that. It would be a bummer if that is the case. Something I will need to look into. If you don't need margin and are not trading the underlying asset (which I could see being a problem), then I don't see what the problem is. But I shall see. Thanks. Depending on the day and even time, you'd get your $2 profit less the $5 commission. Jack's warning is correct, but more so for thinly traded options, either due to the options having little open interest or the stock not quite so popular. In your case you have a just-in-the-money strike for a highly traded stock near expiration. That makes for about the best liquidity one can ask for.  One warning is in order - Sometime friday afternoon, there will be a negative time premium. i.e. the bid might seem lower than in the money value. At exactly $110, why would I buy the option? Only if I can buy it, exercise, and sell the stock, all for a profit, even if just pennies. "In real life, you'd see spreads like AMZN 04/13/2017 910.00 C 4.90 +1.67 Bid: 4.75 Ask: 5.20 (with AMZN @ $897 right now) and the fill you'd get on the buy side would be closer to the ask. i.e. I'd offer $5.00 and hope that it filled.  Filling a $4 bid when ask is $8 isn't likely unless the stock blipped down enough for your price to fill.  Options are a lot like day trading, in most cases. Most members here will agree that day trading isn't investing, it's gambling. Long term, the S&P has been up 10%/yr. But any given day, the noise of the market is a 50/50 zero sum game. Most long term stock 'investors' do well. Those who get in and out, not so much.  There are aspects to options that are appealing. As you've seen, the return can be high, even IRL, but your loss can be 100% as well. Let me share with you a blurred line - I wrote ""Betting on Apple at 9 to 2"" in which I described an option strategy that ran 2 years and would return $10,000 on a $2200 bet. A similar bet that ended a year ago yielded a 100% loss. I don't post there very often, as I keep that trading to a minimum.  There are warnings for those who want to start trading options -"