How much principal do I get back with a target-maturity ETF?
Adding a couple more assumptions, I'd compute about $18.23 would be that pay out in 2018.  This is computed by taking the Current Portfolio's Holdings par values and dividing by the outstanding shares(92987/5100 for those wanting specific figures used). Now, for those assumptions: Something to keep in mind is that bonds can valued higher than their face value if the coupon is higher than other issues given the same risk.  If you have 2 bonds maturing in 3 years of the same face value and same risk categories though one is paying 5% and the other is paying 10% then it may be that the 5% sells at a discount to bring the yield up some while the other sells at a premium to bring the yield down.  Thus, you could have bonds worth more before they mature that will eventually lose this capital appreciation.
Right now, the unrealized appreciation of Vanguard Tax-Managed   Small-Cap Fund Admiral Shares is 28.4% of NAV. As long as the fund   delivers decent returns over the long term, is there anything stopping   this amount from ballooning to, say, 90% fifty years hence? I'd have a heck of a time imagining how this grows to that high a number realistically.  The inflows and outflows of the fund are a bigger question along with what kinds of changes are there to capital gains that may make the fund try to hold onto the stocks longer and minimize the tax burden. If this happens, won't new investors be scared away by the prospect of   owing taxes on these gains? For example, a financial crisis or a   superior new investment technology could lead investors to dump their   shares of tax-managed index funds, triggering enormous capital-gains   distributions. And if new investors are scared away, won't the fund be   forced to sell its assets to cover redemptions (even if there is no   disruptive event), leading to larger capital-gains distributions than   in the past? Possibly but you have more than a few assumptions in this to my mind that I wonder how well are you estimating the probability of this happening. Finally, do ETFs avoid this problem (assuming it is a problem)? Yes, ETFs have creation and redemption units that allow for in-kind transactions and thus there isn't a selling of the stock.  However, if one wants to pull out various unlikely scenarios then there is the potential of the market being shut down for an extended period of time that would prevent one from selling shares of the ETF that may or may not be as applicable as open-end fund shares. I would however suggest researching if there are hybrid funds that mix open-end fund shares with ETF shares which could be an alternative here. I'll offer another answer, using different figures. Let's assume 6% is the rate of return you can expect.  You are age 25, and plan to retire at age 65.  If you have $0 and want $1M at retirement, you will need to put away $524.20/month, or $6,290.40/year, which is 15% of $41,936.  So $41,936 is what you'd need to make per year in order to get to your target. You can calculate your own figures with a financial calculator:  480 months as your term (or, adjust this to your time horizon in months), .486755% as your interest (or, take your assumed interest rate + 1 to the 1/12th power and subtract 1 to convert to a monthly interest rate), 0 as your PV, and $1M as your FV; then solve for PMT. Real world example.    AGNC = 21.79 time of post.  Upcoming .22 cents ex-div Mar 27th Weekly options Mar 27th - $22 strike put has a bid ask spread of .22 / .53. If you can get that put for less than .21 after trade fee's, you'll have yourself a .22 cent arbitrage.   Anything more than .21 per contract eats into your arbitrage.  At .30 cents you'll only see .13 cent arbitrage.  But still have tax liability on .22 cents.  (maybe .05 cents tax due to REIT non-exempt dividend rates)  So that .13 gain is down to a .08 cents after taxes. Say one makes $60k/yr. The net gain is that half these funds are received about 2 weeks prior. To keep the math simple, let's assume a 12% return per year on the funds during this time. $30K * 12% is $3600. But 2 weeks is about 4% of a year, so $144. That's at a 12% return. In an offset mortgage the return will be closer to 4%, a $48/yr benefit.  With short term rates at or below 1%, we're really looking at a gain of $12 or so for the extra time with the funds. The Creation/Redemption mechanism is how shares of an ETF are created or redeemed as needed and thus is where there can be differences in what the value of the holdings can be versus the trading price. If the ETF is thinly traded, then the difference could be big as more volume would be where the mechanism could kick in as generally there are blocks required so the mechanism usually created or redeemed in lots of 50,000 shares I believe. From the link where AP=Authorized Participant: With ETFs, APs do most of the buying and selling. When APs sense   demand for additional shares of an ETF—which manifests itself when the   ETF share price trades at a premium to its NAV—they go into the market   and create new shares. When the APs sense demand from investors   looking to redeem—which manifests itself when the ETF share price   trades at a discount—they process redemptions. So, suppose the NAV of the ETF is $20/share and the trading price is $30/share. The AP can buy the underlying securities for $20/share in a bulk order that equates to 50,000 shares of the ETF and exchange the underlying shares for new shares in the ETF. Then the AP can turn around and sell those new ETF shares for $30/share and pocket the gain. If you switch the prices around, the AP would then take the ETF shares and exchange them for the underlying securities in the same way and make a profit on the difference. SEC also notes this same process. You've got the right idea, except that the stated interest rate is normalized for a 1-year investment.  Hence if you buy a 4-week bill, you're getting something closer to 4/52 of what you've computed in your question.  More precisely, the Treasury uses a 360 day year for these calculations, so you multiply the stated rate by (number of days until maturity)/360 to get the actual rate of return. I-series Treasury bonds are the closest thing you can get to an investment where your principal is guaranteed to be returned (even accounting for inflation).  https://www.treasurydirect.gov/indiv/research/indepth/ibonds/res_ibonds.htm Treasury Inflation Protected Securities are another option, but if you have to sell before maturity then 'the market' may not pay you back your initial investment.  https://www.treasurydirect.gov/indiv/products/prod_tips_glance.htm "I wonder if ETF's are further removed from the actual underlying holdings or assets giving value to the fund, as compared to regular mutual funds. Not exactly removed. But slightly different. Whenever a Fund want to launch an ETF, it would buy the underlying shares; create units. Lets say it purchased 10 of A, 20 of B and 25 of C. And created 100 units for price x. As part of listing, the ETF company will keep the purchased shares of A,B,C with a custodian. Only then it is allowed to sell the 100 units into the market. Once created, units are bought or sold like regular stock. In case the demand is huge, more units are created and the underlying shares kept with custodian.  So, for instance, would VTI and Total Stock Market Index Admiral Shares be equally anchored to the underlying shares of the companies within the index? Yes they are. Are they both connected? Yes to an extent. The way Vanguard is managing this is given a Index [Investment Objective]; it is further splitting the common set of assets into different class. Read more at Share Class. The Portfolio & Management gives out the assets per share class. So Vanguard Total Stock Market Index is a common pool that has VTI ETF, Admiral and Investor Share and possibly Institutional share. Is VTI more of a ""derivative""? No it is not a derivative. It is a Mutual Fund." No that is your implicit return if you hold it to maturity per year. That yield is quoted per annum. You will receive semi-annual payments base on the coupon of whatever off the run 10yr you buy. If your coupon is 2% then you will receive $10 bi-yearly. Mind you, buying a 10 year in this environment will yield a negative real return, meaning after inflation over 10 years you will have your entire principal back, but inflation adjusted it will have less purchasing power than today, meaning there isn't enough yield to make the purchase worth it.  Also about your upward slope question, yes the 30 will yield more than the 2,5,7,10. This is because longer time means more risk. Will in the future the USA be perceived as near riskless? There is also interest rate risk, and liquidity risk. You could use  the Gordon growth model implied expected return: P = D/(r-g) --&gt; r = D/P (forward dividend yield) + g (expected dividend growth). But obviously there is no such thing as a good market return proxy. "Generally, ETFs work on the basis that there exists a pair of values that can be taken at any moment in time: A Net Asset Value of each share in the fund and a trading market price of each share in the fund.  It may help to picture these in baskets of about 50,000 shares for the creation/redemption process. If the NAV is greater than the market price, then arbitrageurs will buy up shares at the market price and do an ""in-kind"" transaction that will be worth the NAV value that the arbitrageurs could turn around and sell for an immediate profit. If the market price is greater than the NAV, then the arbitrageurs will buy up the underlying securities that can be exchanged ""in-kind"" for shares in the fund that can then be sold on the market for an immediate profit. What is the ETF Creation/Redemption Mechanism? would be a source on this though I imagine there are others. Now, in the case of VXX, there is something to be said for how much trading is being done and what impact this can have. From a July 8, 2013 Yahoo Finance article: At big option trade in the iPath S&P 500 VIX Short-Term Futures Note   is looking for another jump in volatility.  More than 250,000 VXX options have already traded, twice its daily   average over the last month. optionMONSTER systems show that a trader   bought 13,298 August 26 calls for the ask price of $0.24 in volume   that was 6 times the strike's previous open interest, clearly   indicating new activity. Now the total returns of the ETF are a combination of changes in share price plus what happens with the distributions which could be held as cash or reinvested to purchase more shares." You have to call Interactive Brokers for this. This is what you should do, they might even have a web chat. These are very broker specific idiosyncrasies, because although margin rules are standardized to an extent, when they start charging you for interest and giving you margin until settlement may not be standardized. I mean, I can call them and tell you what they said for the 100 rep. Yes, it can buy back the call, but much before stock hits the $30 mark.   Let us say you got 1$ from selling the call. So the total money in your account is 4$ + 1 $ = 5 $. When stock hits 10$ (your strike), the maintenance margin is 5$. As soon as stock goes past 10, your maintenance margin is violated. So broker will buy back your call (at least IB does that, it does not wait for a margin call). Now if the stock gapped up from 8 to 30,then yes, broker will buy it back at 30, so your account will have a negative balance. Assume the call cost 20$ when stock hit 30, your balance is: 5 - (30-10) = -15. Depending on broker, I suppose they will ask you to bring your account balance back up to positive. If they don't do that, they risk going out of business. There isn't a single hard and fast return to expect. Securities, like all things in a free market, compete for your money. As the Fed sets the tone for the market with their overnight Fed funds rate, you might want to use a multiple of the 'benchmark' 10-year T-note yeald. So let's suppose that a good multiple is four. The current yeald on the 10-year T-note is hovering around two. That would give a target yeald of eight.  http://stockcharts.com/h-sc/ui?s=%24UST10Y&p=W&b=5&g=0&id=p47115669808 One strategy to consider is a well-diversified index fund of equities. These have historically averaged 7-8% real growth. So withdrawing 3% or 4% yearly under that growth should allow you to withdraw 30+ years with little risk of drawing down all your capital. As a bonus you're savings target would come down from $10 million to $2.5 million to a little under $3.5 million.