Auto balancing portfolio through new purchases
"Finding the ""optimal"" solution (and even defining what optimal is) would probably take a lot of searching of all the possible combinations of stocks you could buy, given that you can't buy fractional shares. But I'd guess that a simple ""greedy"" algorithm should get you close enough. For any given portfolio state, look at which stock is furthest below the target size - e.g. in your example, S3 is 3.5% away whereas S1 is only 3.1% away and S2 is over-sized. Then decided to buy one stock of S3, recalculate the current proportions, and repeat until you can't buy more stocks because you've invested all the money. If you have to pay a transaction fee for each kind of stock you purchase you might want to calculate this in larger lot sizes or just avoid making really small purchases."
Personally, I don't think that the interest from the car loan is worth the credit history you're building through it. There are other ways to build credit that don't require you to pay interest, like the credit card you mentioned (so long as you keep paying off the balance). So I'd go that route: ditch the auto loan and replace it with a line of consumer credit. Just be careful not to overspend because the card will likely have a higher interest rate than your loan. Rule of thumb, the earlier you pay down your balance, the less interest you will accrue and the faster you will pay off the debt as a whole. But lets play with some real numbers here.  You cited $5000 balance and a $750 payment, but with various bills and things adding onto the balance over the course of a month. Now if your purchases and payments add up to the same number, you are in a losing game, so for the sake of argument I am going to say you are putting $500 + interest on the card each month and making a $750 payment.  We also need an interest rate to work with, I am going to use 1%/month and 30 day months to keep the math a bit easier to follow.   You basically have two choices in this scenario, you can pay 750 a month on the card, then use it to make your $500 in purchases/other payments over time as you suggest in your question.  Or you can pay $250, and hold back $500 to make those other payments directly without running them through the card, as has been suggested in some other answers. So let us compare the two... If I start the cycle at $5000, make a $250 payment on the first day of the cycle, then have no other activity, I will have a balance of $4750 for the month and accrue $47.50 in interest at the close of the cycle.  Balance going into the next period is now $4797.50.  Carry this out for a year, and your balance at the close of the 12th cycle is $2431.79, and $431.79 of your payments went to interest. By contrast, if you pay $750 at the start of the month, then add $100 back every 6 days so that you spend $500 over the course of the cycle. You will have an average daily balance of $4466.67, which results in $44.67 in interest charges being accrued at the end of the month.  This gives you a balance of $4794.67 going into the next cycle, putting you about $3 ahead of the previous method.  Push this pattern out for a year and your ending balance is 2395.86, with 395.86 going to interest.  Resulting in a savings of ~$36 over making the smaller payment and paying cash for your other expenses.  If this happens to be a rewards card, you also have gained whatever rewards benefit it gives you. This demonstrates that by the strict numbers game, the scenario you propose should come out a small but measurable distance ahead of making a smaller payment in order to avoid putting things back on the card.  So why do so many people adamantly advise you to not do this?   Most of it has to do with psychology and risk.  The cash method does not leave any room for you to over spend.  You have shredded or locked up the credit card so it can’t be used casually, and when you run out of cash, you can’t spend any more.  Which forces you to pay much closer attention to where your money is going.   When you are running things through the credit card, you generally don’t have that hard stop unless you are up against your credit limit, and even then most issuers are quite happy to let you go over and charge you extra fees for doing so.  So if you have this plan where you are intending to put $500 on the card in a month, then lose track of something you did early in the month, and inadvertently spend $800, you are digging yourself deeper into the hole instead of climbing your way out. There is also a risk in terms of income loss.  In the cash method, you no longer have the money to spend, and you are forced to make the hard decisions about where to allocate what you do have, making you much more likely to cut back on luxury items to preserve the necessities.  In the card method, it is easy to say “eh, the card has room, I can catch up again later” and not realize the mess you are causing yourself until you are in way over your head.  I personally have run all my bills through a credit card in the past so that I could have one single payment to make.  Then I was unemployed for six months, and ended up moving before I found a new job.  Everything in between, including the move, went on the card.  Next thing I know I am carrying a balance of $15k where I used to always have it paid in full.  It took roughly 10 years, including several years of working strictly in cash, to get that back under control. I currently have a card that is carrying a balance, and I am running select expenses (such as fuel and food) through it while I whittle the balance back down.  Most of my main bills are still paid directly from cash, specifically so that I don’t fall back into the same trap I did before.  Even so, there were several months in the past year where the balance was creeping up instead of down, because we were not paying that close of attention to our spending.   Then my wife lost her job, and it forced us to closely evaluate where our money was going.  We still run certain things through said card, but we are much stricter about it being only those select things, and the balance is trending down again.  The main reason we are still channeling those expenses that way is because this is a cash back reward card, and we will be getting roughly $1000 back here in a couple more months. "Value averaging has you shift the balance of your portfolio over time, not the amount of contributions.  So you can only do it if you have a portfolio holding both risky assets (shares etc) and some cash. You start out by making a plan about how much you will contribute every month and at what rate you expect the share part of the portfolio to grow.  Perhaps based on 20th century data you think an 8% growth rate is reasonable.  Or alternatively if you know your desired final amount obviously you can work backwards to a desired rate from that. If in any month the share part is falling below its expected growth path, you would put more money into it: possibly your whole paycheck contribution plus some from the savings cash account.  On the other hand if the share component is growing ""too fast"" you would put all your additional savings into cash.  So if your investments are doing well, you're not supposed to spend the excess money, but rather to put it aside into a dedicated cash account to top up your share component when prices fall. In theory, this has the auto-levelling benefit of Dollar Cost Averaging, but even better: when prices are high, you'll automatically buy fewer shares, or even sell some; conversely when prices are low you'll buy extra shares from your reserve account. If it turns out your estimate was unreasonably optimistic, and over your lifetime shares only ever average 3%, you'll end up with an entirely share portfolio, and a bumpier ride than you might have liked.  If you have horrible luck and over your entire investing life shares return less than cash (which has happened, though not yet in the USA), then this will be worse than a standard balanced portfolio. The original book Value Averaging by Edelson has a pretty good explanation of various cases, though I would say some of the examples are worked in excessive detail. I have not implemented this myself, one reason being that the amount I'm able to save from year to year varies, as it probably does for you, and so predicting a path is not quite so simple as he assumes.  You could still do it I suppose. I think you could get a very crude approximation to this by simply directing your savings into cash when the share market's rate of growth over the last several years is above what you think is the long term average." "If the stock market dropped 30%-40% next month, providing you with a rare opportunity to buy stocks at a deep discount, wouldn't you want to have some of your assets in investments other than stocks? If you don't otherwise have piles of new cash to throw into the market when it significantly tanks, then having some of your portfolio invested elsewhere will enable you to back up the proverbial truck and load up on more stocks while they are on sale. I'm not advocating active market timing. Rather, the way that long-term investors capitalize on such opportunities is by choosing a portfolio asset allocation that includes some percentage of safer assets (e.g. cash, short term bonds, etc.), permitting the investor to rebalance the portfolio periodically back to target allocations (e.g. 80% stocks, 20% bonds.) When rebalancing would have you buy stocks, it's usually because they are on sale. Similarly, when rebalancing would have you sell stocks, it's usually because they are overpriced. So, don't consider ""safer investments"" strictly as a way to reduce your risk. Rather, they can give you the means to take advantage of market drops, rather than just riding it out when you are already 100% invested in stocks. I could say a lot more about diversification and risk reduction, but there are plenty of other great questions on the site that you can look through instead." If you have 100% of your money in one security that is inherently more risky than splitting your money 50/50 between two securities, regardless of the purported riskiness of the two securities. The calculations people use to justify their particular breed of diversification may carry some assumptions related risk/reward calculations.  But these particular justifications don't change the fact that spreading your money across different assets protects your money from value variances of the individual assets.  Splitting your $100 between Apple and Microsoft stock is probably less valuable (less well diversified) than splitting your money between Apple and Whole Foods stock but either way you're carrying less risk than putting all $100 in to Apple stock regardless of the assumed rates of return for any of these companies stock specifically. Edit: I'm sure the downvotes are because I didn't make a big deal about correlation and measuring correlation and standard deviations of returns and detailed portfolio theory.  Measuring efficacy and justifying your particular allocations (that generally uses data from the past to project the future) is all well and good.  Fact of the matter is, if you have 100% of your money in stock that's more stock risk than 25% in cash, 25% in bonds and 50% in stock would be because now you're in different asset classes.  You can measure to your hearts delight the effects of splitting your money between different specific companies, or different industries, or different market capitalizations, or different countries or different fund managers or different whatever-metrics and doing any of those things will reduce your exposure to those specific allocations.   It may be worth pointing out that currently the hot recommendation is a plain vanilla market tracking S&P 500 index fund (that just buys some of each of the 500 largest US companies without any consideration given to risk correlation) over standard deviation calculating actively managed funds.  If you ask me that speaks volumes of the true efficacy of hyper analyzing the purported correlations of various securities. Slice and Dice would have the approach for dividing things up into 25% of large/small and growth/value that is one way to go. Bogleheads also have more than a few splits ranging from 2 funds to nearly 10 funds on high end. "Modern portfolio theory dramatically underestimates the risk of the recommended assets.  This is because so few underlying assets are in the recommended part of the curve.  As investors identify such assets, large amounts of money are invested in them.  This temporarily reduces measured risk, and temporarily increases measured return.  Sooner or later, ""the trade"" becomes ""crowded"".  Eventually, large amounts of money try to ""exit the trade"" (into cash or the next discovered asset).  And so the measurable risk suddenly rises, and the measured return drops. In other words, modern portfolio theory causes bubbles, and causes those bubbles to pop. Some other strategies to consider:" An ETF manager will only allow certain financial organisations to create and redeem ETF shares.  These are called Authorised Participants (APs).  The APs have the resources to bundled up packages of shares that they already own and hold in order to match the ETFs requirements.  In the case of the EDEN ETF, this portfolio is the MSCI Denmark Index.  Only APs transact business directly with the ETF manager.   When ETF shares need to be created, the AP will bundle up the portfolio of shares and deliver them to the ETF manager.  In return, the ETF manager will deliver to the AP the corresponding number of shares in the ETF.  Note that no cash changes hands here. (These ETF shares are now available for trading in the market via the AP.  Note that investors do not transact business directly with the ETF manager.) Similarly, when ETF shares need to be redeemed, the AP will deliver the ETF shares to the ETF manager.  In return, the ETF manager will deliver to the AP the corresponding portfolio of shares.  Again, no cash changes hands here. Normally, with an established and liquid ETF, investors like you and me will transact small purchases and sales of ETF shares with other small investors in the market.  In the event that an AP needs to transact business with an  investor, they will do so by either buying or selling the ETF shares.  In the event that they have insufficient ETF shares to meet demand, they will bundle up a portfolio deliver them to the ETF provider in return for ETF shares, thus enabling them to meet demand.  In the event that a lot of investors are selling and the AP ends up holding an excessive amount of ETF shares, they will deliver unwanted shares to the ETF manager in exchange for a portfolio of the underlying shares. According to this scheme, large liquidations of ETF holdings should not effect the share prices of the underlying portfolio.  This is because the underlying shares are not sold in the market, rather they are simply returned to the AP in exchange for the ETF shares (Recall that no cash is changing hands in this type of transaction).   The corresponding trail of dividends and distributions to ETF share holders follows the same scheme.