IRR vs. Interest Rates
Yes, if your IRR is 5% per annum after three years then the total return (I prefer total rather than your use of actual) over those three years is 15.76%. Note that if you have other cashflows in and out, it gets a bit more complicated (e.g. using the XIRR function in Excel), but the idea is to find an effective annual percentage return that you're getting for your money. IRR is not subjective, this is a response to @Laythesmack, to his remark that IRR is subjective. Not that I feel a need to defend my position, but rather, I'm going to explain his.  My company offered stock at a 15% discount. We would have money withheld from pay, and twice per year buy at that discount. Coworkers said it was a 15% gain. I offered some math. I started by saying that 100/85 was 17.6%, and that was in fact, the gain. But, the funds were held by the company for an average of 3 months, not 6, so that gain occurred in 3 months and I did the math 1.176^4 and resulted in 91.5% annual return. This is IRR.  It's not that it's subjective, but it assumes the funds continue to be invested fully during the time. In our case the 91.5% was real in one sense, yet no one doubled their money in just over a year.  Was the 91% useless? Not quite. It simply meant to me that coworkers who didn't participate were overlooking the fact that if they borrowed money at a reasonable rate, they'd exceed that rate, especially for the fact that credit lines are charged day to day. Even if they borrowed that money on a credit card, they'd come out ahead.  IRR is a metric. It has no emotion, no personality, no goals. It's a number we can calculate. It's up to you to use it correctly. Yes, assuming that your cash flow is constantly of size 5 and initial investment is 100, the following applies: IRR of 5% over 3 years: Value of CashFlows: 4.7619 + 4.5351 + 4.3192 = 13.6162 NPV: 100 - 13.6162 = 86.3838 Continuous compounding: 86.3838 * (1.05^3) = 100 IRR is subjective, if you could provide another metric instead of the IRR; then this would make sense. You can't spend IRR. For example, you purchase a property with a down payment; and the property provides cash-flow; you could show that your internal rate of return is 35%, but your actual rate of importance could be the RoR, or Cap Rate. I feel that IRR is very subjective. IRR is hardly looked at top MBA programs. It's studied, but other metrics are used, such as ROI, ROR, etc. IRR should be a tool that you visually compare to another metric. IRR can be very misleading, for example it's like the cash on cash return on an investment.
Your hypothetical money market account parallel basically nails it.  You understand exactly how the math works.  IRR computes a rate at which your money market account would have to pay interest in order to match whatever investment you are comparing to. That said, there are two major complicating factors to consider: Your hypothetical account would have to not only pay interest, but also lend money, at exactly the IRR rate.  In reality of course, it never happens this way.  You may be able to lend (invest) at x, but to borrow you're going to have to pay y.  IRR simplifies away that issue in order to give us a single number.  That number can be very handy for comparison to other competing hypothetical investments, but it does not capture that fundamental issue of lending rate vs. borrowing rate. An IRR calculation assumes implicitly that all cash flows, outgoing and incoming, are known and fixed; that is, risk-free.  It makes no allowance whatever for risk, and all investments have some level of risk.  Two investments that compute to the same IRR might have hugely different risk around their cashflows, and so not be a close decision at all.  To compare those investments, you might go to a measure like RAROC-- risk-adjusted return on capital.  But that's much harder, and more subjective, because it requires some numerical measurement of risk. I realize this question is a few years old now, but I wanted to address one of the OP's questions that hadn't been answered yet (my answer is framed as though the question were recent): However, on the plus side, the monthly payment would likely be $200 less/mo with this house vs our current rent. On a 30 year mortgage it would be almost $3-400 less. This makes me think that I could use the difference to pay directly toward the principal each month. Is my logic sound? The way amortization works, if the interest rate between 30 and 15 were the same, then making principal-only prepayments on the 30 year to cover the difference in monthly payments would result in the exactly the same schedule as if you did minimum payments on the 15-year - i.e. the numbers would be practically indistinguishable.  Of course, in practice the interest rate is slightly better on the 15-year, which makes the 30-year with prepayments compare slightly less favorably. If you're confident that you'll be able to reliably keep up with the monthly payments, the 15-year would minimize the total amount of interest you pay, and help you get off of PMI slightly faster.  But the 30-year w/ prepayments gives you the option to skip a prepayment or two if you run into any financial difficulty, which is a nice option to have.  But you do have to be disciplined about making the prepayments every month. I will attempt to answer three separate questions here: The standard answer is that an emergency fund should not be in an investment that can lose value.  The safest course of action is to put it in a savings account or other very low risk investment somewhere. This question becomes: can a reasonable and low risk investment in Sweden be comparable to or better than a low risk investment in Brazil? Inflation in Brazil has averaged a little less than 6% over the last 10 years with a recent spike up above 8%.  A cursory search indicates interest rates on savings accounts in Brazil are outpacing inflation so you might still expect a positive return on money in a savings account there. By contrast, Sweden's inflation rate has been around 1% over the last 10 years and has hovered around 0 or even deflation in recent years.  Swedish interest rates for savings accounts right now are very low, nearly 0%.  Putting money in a savings account in Sweden would likely hold its value or lose a slight amount of value. Based on this, you might be better off leaving your emergency fund invested in BRL in Brazil. The answer to this a little unclear.  The Brazilian stock market has been all over the place in the last 10 years, with a slight downard trend in recent years.  In comparison, Sweden's stock market has shown fairly consistent growth in spite of the big dip in 2008.  Given this, it seems like the fairest comparison would your current 13% ROI investment in Brazil vs. a fund or ETF that tracks the Swedish stock market index. If we assume a consistent 13% ROI on your investment in Brazil and a consistent inflation rate of 6%, your adjusted ROI there would be around 7% per year. The XACT OMS30 ETF that tracks the Swedish OMS 30 Index has a 10 year annualized return of 9.81%.  If you subtract 0.8% inflation, you get an adjusted ROI 9%. Based on this, Sweden may be a safer place for longer term, moderate risk investments right now. What asset allocation is right for you (at the most basic the percentage if stocks vs bonds; at the advanced level, percentage of growth vs value, international vs domestic etc) is a function of your age, retirement goals, income stability and employment prospects until retirement.  Roth IRA is orthogonal to this.  Now, once you have your allocation worked out there are tactical tax advantage decisions available: interest income, REIT and MLP dividends are taxed at income and not capital gains rate, so the tactical decision is to put these investments in tax advantage accounts like Roth and 401ks.  Conversely, should you decide to buy and hold growth stocks there are tactical advantages to keeping them in a taxable account: you get tax deferment until the year you choose to sell (barring a takeover), you get the lower lt cap gains rate, and you can employ tax loss harvesting. Talk about coincidence, we just recieved letters from our bank saying that our interest only loans will be going up by 0.46% and if we want to keep our lower rate we will need to change early to P&I. Now our Interest only periods end in 6 months to about 16 months anyway. We have decided to change to P&I early and save on our interest expenses. Why? Because the main purpose of investing is to make money not to save on tax. Even if you are on the highest marginal tax rate for every extra dollar of expenses you spend and claim as a deduction you will only get about 50 cents back through tax savings. If you are on the lowest marginal tax rate your tax savings will reduce to less than 20 cents for every extra dollar spent. If you are investing in order to save on tax you may be investing for the wrong reasons. Your primary reason for investing should be to make money, for wealth creation. A good reason to stay with an Interest only loan for an investment property would be if you require the extra cash flow you would receive compared with an I&P loan. When you buy a bond - you're giving a loan to the issuer. The interest rate on the bond is the interest rate on the loan. Usually (and this is also the case with the treasury bonds), the rate is fixed for the term of the loan. Thus, if the market rate for similar loans a year later is higher, the rate for the loan you gave - remains the same. That's a rearrangement of the fisher equation; which is the correct way to determine real rates.  However, people often use the approximation real ≈ nominal - inflation; and if you're doing this for homework on software that is looking for exactly 1 numerical answer, they may be expecting you to use that instead.  Real interest rate is less formal nomenclature and refers to using the approximation.  Inflation-adjusted return is the fisher equation.   In the real world you will use the approximation when you're figuring out a real rate while you're talking mid-sentence during a meeting; and use the fisher equation in spreadsheets/calculations. The key thing to consider in a question like this is, What return am I getting on my investment versus what interest am I paying on the loan? If the investment returns more than what you're paying on the loan, than it makes sense to keep the investment and pay off the loan with other income. If the investment returns less, than it makes sense to cash it out to pay off the loan. One complicating factor is taxes. In the case of an IRA, you're not paying taxes on the profits. You do pay a tax penalty for an early withdrawal. Those are both factors that tend to make keeping the money in the IRA more desirable. And of course, if the choice is between keeping your investment and defaulting on the loan, you probably want to close out the investment. I don't know what return you're getting on your IRA, but it's probably more than 6.8%. I'd have to check but I think my retirement funds got over 20% last year. If you're not getting 6.8%, you might want to investigate switching to another investment fund. I'm sure there's a lot I don't know about your situation, but I'd think that keeping the IRA would be a better plan. If you can't add to it for some time well you get these debts paid off, well, that's how it is.