Why use ROI if I can use effective compount interest?
Yes though I'd likely put a caveat on that. If you take short-term investments and extrapolate the results to get an annual result this can be misleading. For example, if a stock goes up 10% in a month, assuming this will continue for the next 11 months may not be a great idea. Thus, beware of how much data do you have in making these calculations. When looking at long-term investments, the compound annual growth rate can be quite useful for comparison.
"Complex matter that doesn't boil down to a formula.   The quant aspect could be assessed by calculating WACCs under various funding scenarii and trying to minimize, but it is just one dimension of it.  The quali aspects can vary widely depending on the company, ownership structure, tax environment and business needs and it really can't be covered even superficially in a reddit comment...  Few examples from the top of my mind to give you a sense of it:  - shareholders might be able to issue equity but want to avoid dilution, so debt is preferred in the end despite cost. Or convertible debt under the right scenario.  - company has recurring funding needs and thinks that establishing a status on debt market is worth paying a premium to ensure they can ""tap"" it whenever hey need to.  - adding debt is a way to leverage and enhance ROI/IRR for certain types of stakeholders (think LBOs)  - etc etc etc  Takes time and a lot of experience/work to be able to figure out what's best and there isn't always a clear answer.  Source: pro buy side credit investor with experience and sizeable AuMs." Yes. Using debt appropriately is a huge part of what's called optimal capital structure theory in the finance world. Debt is generally cheaper than equity financing due to the tax deductibility of interest and using it appropriately can really juice the profitability of a business as long as the rate of return on equity in the business exceeds the interest rate on the debt. P/E ratio is useful but limited as others have said. Another problem is that it doesn't show leverage. Two companies in the same industry could have the same P/E but be differently leveraged. In that case I would buy the company with more equity and less debt as it should be a less risky investment. To compare companies and take leverage/debt into account you could use the EV/EBIT ratio instead. Its slightly more complicated to calculate and isn't presented by as many data sources though. Enterprise Value (EV) can be said to represent the value of the company if someone would buy it today and then pay off all its (interest bearing) debt. EV is essentially calculated like this: (Market Capitalization plus cash & cash equivalents)  minus interest-bearing debt.  This is then divided by EBIT (Earnings before interest and tax) to get the ratio. One drawback of this ratio though is that it can't be used for financials since their balance sheet pretty much consists of debt and the Enterprise Value therefore doesn't tell us very much. Also, like the P/E ratio it is dependent on fresh numbers. A balance sheet is just a glimpse of the companys financial situation on ONE DAY, and this could (and probably will, although not drastically for bigger companies) change to the next day. "Hi, accounting major here!  A lot of people mentioned both tax advantages and ""cheap"" money (money you can borrow at a low interest rate).  Another reason businesses do this is to reward investors. Generally people with stock in a company want to see some of its operations financed with debt, instead of all of it financed from investors' money or profit. This way the company can grow more and still pay better dividends to its investors. However, you don't want too much debt either. It's a balance, and a way to see how much debt vs equity a company has is called a leverage ratio (leverage=debt). Hope this helps!" "An asset allocation formula is useful because it provides a way to manage risk. Rebalancing preserves your asset allocation. The investment risk of a well-diversified portfolio (with a few ETFs or mutual funds in there to get a wide range of stocks, bonds, and international exposure) is mostly proportional to the asset class distribution. If you started out with half-stocks and half-bonds, and stocks surged 100% over the past few years while bonds have stayed flat, then you may be left with (say) 66% stocks and 33% bonds. Your portfolio is now more vulnerable to future stock market drops (the risk associated with stocks). (Most asset allocation recommendations are a little more specific than a stock/bond split, but I'm sure you can get the idea.) Rebalancing can be profitable because it's a formulaic way to enforce you to ""buy low, sell high"". Massive recessions notwithstanding, usually not everything in your portfolio will rise and fall at the same time, and some are actually negatively correlated (that's one idea behind diversification, anyway). If your stocks have surged, chances are that bonds are cheaper. This doesn't always work (repeatedly transferring money from bonds into stocks while the market was falling in 2008-2009 could have lost you even more money). Also, if you rebalance frequently, you might incur expenses from the trading (depending on what sort of financial instrument you're holding). It may be more effective to simply channel new money into the sector that you're light on, and limit the major rebalancing of the portfolio so that it's just an occasional thing. Talk to your financial adviser. :)" Depending on the improvement, you have to amortize or depreciate it over time, which effectively allows you to write off the value over a period of years, even if you pay for it all up front. This messes with cash flow, which is different than profitability, but when you span the write off over five or ten years, the distinction between cash flow and profitability for a private, self funded company is irrelevant. If the money ain't there, the money ain't there. Operating capital is life blood.  Taxes also alter the ROI equation of the investment, since you don't keep all the money you put in.  Way over simplified example: Lets say I close out the year with some arbitrary profit - ten million bucks - in my war chest. 3.5 could go to taxes. I also know that my supplier can't handle my volume for next year while the season is hot, so I'd like to buy inventory in the off season. Last year I sold 6.5 mill worth of stuff from this supplier, but I estimate I could sell 9-10 mill if I didn't have availability problems. If I buy 9-10 mill in inventory, I can't pay taxes. If I pay taxes, I can't buy enough to grow next year.   Sure, COGS is a deductible expense, but the expense isn't realized until the inventory is sold, which won't be until long after these taxes are due.  I now have taxes interfering with my expansion, even though eventually I can write that off.  Now lets look at the manufacturer - sure he could expand his capacity and make more money, but he has to deduct the 5 mill machine he needs over twenty years (or ten or whatever) while the purchase price needs to be made today. This year he's gonna pay tax on 90 or 95% of the money he used to buy that machine, which would eat into the money he needs to buy raw materials to fill orders he already has.  Of course, the real world is much more complicated, and you can leverage leasing agreements and purchasing terms to alleviate this to some extent, but I wanted to illustrate a point. I hope my extremely simplified example communicated what I mean.  Does that make sense? "I don't follow the numbers in your example, but the fundamental question you're asking is, ""If I can borrow money for a low cost, and if I think I can invest it and receive returns greater than that cost, should I do it?"" It doesn't matter where that money comes from, a mortgage that's bigger than it needs to be, a credit card teaser rate, or a margin line from your stock broker. The answer is ""maybe"" - depending on the certainty you have about the returns you'd receive on your investments and your tolerance for risk. Only you can answer that question for yourself. If you make less than your mortgage rates on the investments, you'll wish you hadn't! As an aside, I don't know anything about Belgian tax law, but in US tax law, your deductions can be limited to the actual value of the home. Your law may be similar and thus increase the effective mortgage interest rate." "Accounts track value: at any given time, a given account will have a given value. The type of account indicates what the value represents. Roughly: On a balance sheet (a listing of accounts and their values at a given point in time), there is typically only one equity account, representing net worth, I don't know much about GNUCash, though. Income and expenses accounts do not go on the balance sheet, but to find out more, either someone else or the GNUCash manual will have to describe how they work in detail. Equity is more similar to a liability than to assets. The equation Assets = Equity + Liabilities should always hold; you can think of assets as being ""what my stuff is worth"" and equity and liabilities together as being ""who owns it."" The part other people own is liability, and the part you own is equity. See balance sheet, accounting equation, and double-entry bookkeeping for more information. (A corporate balance sheet might actually have more than one equity entry. The purpose of the breakdown is to show how much of their net worth came from investors and how much was earned. That's only relevant if you're trying to assess how a company has performed to date; it's not important for a family's finances.)" Because a paying down a liability and thus gaining asset equity is not technically an expense, GnuCash will not include it in any expense reports. However, you can abuse the system a bit to do what you want.  The mortgage payment should be divided into principle, interest, and escrow / tax / insurance accounts. For example: A mortgage payment will then be a split transaction that puts money into these accounts from your bank account: For completeness, the escrow account will periodically be used to pay actual expenses, which just moves the expense from escrow into insurance or tax. This is nice so that expenses for a month aren't inflated due to a tax payment being made: Now, this is all fairly typical and results in all but the principle part of the mortgage payment being included in expense reports. The trick then is to duplicate the principle portion in a way that it makes its way into your expenses. One way to do this is to create a principle expense account and also a fictional equity account that provides the funds to pay it: Every time you record a mortgage payment, add a transfer from this equity account into the Principle Payments expense account. This will mess things up at some level, since you're inventing an expense that does not truly exist, but if you're using GnuCash more to monitor monthly cash flow, it causes the Income/Expense report to finally make sense. Example transaction split: I'm not asking if I should carry a balance to the end of the billing period and accrue interest Typically (I say typically because there may be some fringe outlier exception product that begins accruing interest immediately), if you're not carrying a balance already you will not be charged interest for carrying a balance during the billing period.   You accrue a balance, you're issued a statement, if you pay the statement before the due date indicated you don't pay interest; even if your statement balance is less than the current actual balance on the account.  If you carry a balance through that due date you begin to accrue interest.  Not only on the balance carried but on all new charges as well.  But as long as you consistently pay your statement balance before the statement due date you will not be charged any interest. As for a reason why you may want to take advantage of this, simply to ease the administration of your finances.  You just don't need to touch the accounts that frequently to avoid interest charges.  Sure you can let your money sit in an interest bearing account and earn a couple dollars a year but really, you just don't need to focus on your CC charges this frequently. IRR is the acronym for internal rate of return. And it appears that you do understand how it works.  It's not the phrase most investors use for their own returns. I'd typically talk about my own return last year, or over the last decade, etc, as well as what the S&P did during that time, and might even use the term CAGR, compound annual growth rate, although I wouldn't pronounce it 'kegger' or anything like that. Aside from discussing company investments in some MBA class, the only time I'd use IRR is in an excel spreadsheet to calculate the return over time of a series of my own investments.  The nothing magic about this, it's a function of an initial dollar investment, time passing, and the final value. All else is addition complexity based on multiple deposits/withdrawals, etc. If I deposit $100 and get back $200 in a year, it's a 100% IRR.  Disclosure - I am no fan of Investopedia or re-explaining its wording on these topics. I've caught multiple errors in their articles, and unlike the times I've emailed my friends at the IRS who quickly fix typos and mistakes I've caught, Investopedia authors are no better than bloggers (which I am) who take offense at any criticism (which I do not). "TL;DR: Sure, ""do your own homework"" is sometimes a cop out. But that doesn't mean we shouldn't do our homework. I agree that in many cases this is a cop-out by commentators. However, even if you believe in perfect market efficiency, there is benefit in ""doing your homework"" for many reasons. One of which you already mention in the question: different stocks all with the same ""value"" might have widely ranging risk. Another factor that might vary between stocks is their tax consequences. High dividend stocks might be a better fit for some buyers than others. One stock might be priced at $40 because there is a small chance they might get regulatory approval for a new product. This might make this stock very risky with a 20% of being $150 in 12 months, and a 80% chance of being $20. Another stock might be priced at $40 because the company is a cash cow, declining in revenues but producing a large dividend of $0.40 per quarter. Low risk, but also with some potential tax disadvantages. Another stock might be priced at $40 because it's a high growth stock. This would be less risky than the first example, but more risky than the second example. And the risk would be more generalized, i.e. there wouldn't be one day or one event that would be make or break the stock. In short, even if we assume that the market is pricing everything perfectly, not all stocks are equal and not all stocks are equally appropriate to everyone. Sometimes when we hear an analyst say ""they should have done their homework"" they are really saying ""This was a high risk/high reward stock. They should have known that this had a potential downside."" And that all assumes that we believe in 100% pure market efficiency. Which many disagree with, at least to some extent. For example, if we instead subscribe to Peter Lynch's theories about ""local knowledge"", we might believe that everyone has some personal fields of expertise where they know more than the experts. A professional stock analyst is going to follow many stocks and many not have technical experience in the field of the company. (This is especially true of small and mid cap stocks.) If you happen to be an expert in LED lighting, it is entirely feasible (at least to me) that you could be able to do a better job of ""doing homework"" on CREE than the analysts. Or if you use a specialized piece of software from a small vendor at work, and you know that the latest version stinks, then you will likely know more than the analyst does. I think it is somewhat akin to going to a doctor. We could say to ourselves ""the doctor is more knowledgeable about me than medicine, I'm just going to do what they tell me to do."" And 99% of the time, that is the right thing to do. But if we do our ""homework"" anyway, and research the symptoms, diagnoses, and drugs ourselves as well, we can do get benefits. Sometimes we just can express our preferences amongst equal solutions. Sometimes we can ask smarter questions. And sometimes we have some piece of knowledge that the doctor doesn't have and can actually make an important discovery they didn't know. (And, just like investing, sometimes we can also have just enough knowledge to be dangerous and do ourselves harm if we go against the advice of the professionals.)" You're not missing any concepts! It sounds like you are contributing a piece of collateral to the business, and you want to know a fair way to value how much this contribution of collateral is worth. Technically the economic answer would be the difference in interest between a secured loan and an unsecured loan.  So for example suppose that the business could get a loan at 17% without the collateral (maybe just on a credit card) but with the duplex as collateral it is able to get the loan at 10.5%. In principle, the value of this collateral is (17% - 10.5%) or 6.5%, because it has allowed the business to pay 6.5% less interest on its loan. Right, I understand minority interest but it is typically reported as a positive under liabilities instead of a negative. For example, when you are calculating the enterprise value of a company, you add back in the minority interest.    Enterprise Value= Market Share +Pref Equity + Min Interest+ Total Debt - Cash and ST Equivalents.    EV is used to quantify the total price of a company's worth. If you have negative Min Interest on your books, that will make your EV less than it should be, creating an incorrect valuation.   This just doesn't make any sense to me. Does it mean that the subsidiary that they had a stake in had a negative earning? For the purpose of personal finance, treating $500 as Interest Expense is sufficient.  For business accounting, it involves making the $500 a contra-liability and amortizing it as interest expense over the course of life of the loan.