Lend money at a rate linked to the prime rate
Yes.  In the US these are called certificates of deposit or savings accounts.  Every run-of-the-mill bank offers them.  You give the bank money and in return they pay you an interest rate that is some fraction of or (negative) offset from the returns they expect to make from your money. Since most investments that a bank makes (say, loaning money to a local business) are themselves based on some multiple of or (positive) offset from the prime rate, in return the interest rate that they offer you is also mathematically based on the prime rate. You can find lists of banks offering the best returns on CDs or savings accounts at sites like BankRate.
Puerto Rico isn't Algeria. Lending to Algeria is relatively simple as they live and die on the price of oil. Puerto Rico is far more complex and doesn't have a basic resource export economy. Lending to Algeria is a pure oil play and is far less dependent on credit ratings. If Puerto Rico's debt investors take the hit, there isn't a line of lenders throwing money at them. There was this /r/offmychest post yesterday from a person claiming to work for a large investment bank as part of their default risk modelling team. The poster claims that the commercial and real estate lending divisions have been fudging numbers regarding default risks due to a lack of oversight and a bunch of bad commercial loans are about to become due. They further claim that a rise in interest rates could prevent many commercial properties from being able to properly ~~finance~~ refinance their loan. Here is the post: https://www.reddit.com/r/offmychest/comments/77a1vw/i_work_in_bankingfinance_risk_management_i_am/. Any one have any thoughts?            I also found this link on the Mises blog (though it is a year old) that discusses how delinquency rates on commercial and industry loans have been steadily rising since bottoming out in 2015: https://mises.org/blog/delinquency-rates-rising-new-crisis-approaching. Could be something to keep an eye on. I would love to see some more updated data on delinquency. This is a very interesting question. I'm going to attempt to answer it. Use debt to leverage investment. Historically, stock markets have returned 10% p.a., so today when interest rates are very low, and depending on which country you live in, you could theoretically borrow money at a very low interest rate and earn 10% p.a., pocketing the difference. This can be done through an ETF, mutual funds and other investment instruments. Make sure you have enough cash flow to cover the interest payments! Similar to the concept of acid ratio for companies, you should have slightly more than enough liquid funds to meet the monthly payments. Naturally, this strategy only works when interest rates are low. After that, you'll have to think of other ideas. However, IMO the Fed seems to be heading towards QE3 so we might be seeing a prolonged period of low interest rates, so borrowing seems like a sensible option now. Since the movements of interest rates are political in nature, monitoring this should be quite simple. It depends on you. Since interest rates are the opportunity cost of spending money, the lower the interest rates, the lower the opportunity costs of using money now and repaying it later. Interest rates are a market mechanism so that people who prefer to spend later can lend to people who prefer to spend now for the price of interest. *Disclaimer: Historically stocks have returned 10% p.a., but that doesn't mean this trend will continue indefinitely as we have seen fixed income outperform stocks in the recent past. "Banks make less profit when ""long"" rates are low compared to ""short"" rates. Banks lend for long term purposes like five year business loans or 30 year mortgages. They get their funds from (mostly) ""short term"" deposits, which can be emptied in days. Banks make money on the difference between 5 and 30 year rates, and short term rates. It is the difference, and not the absolute level of rates, that determines their profitability. A bank that pays 1% on CDs, and lends at 3% will make money. During the 1970s, short rates kept rising,and banks were stuck with 30 year loans at 7% from the early part of the decade, when short rates rose to double digits around 1980, and they lost money." The equation is the same one used for mortgage amortization.  You first want to calculate the PV (present value) for a stream of $50K payments over 20 years at a10% rate.  Then that value is the FV (future value) that you want to save for, and you are looking to solve the payment stream needed to create that future value. Good luck achieving the 10% return, and in knowing your mortality down to the exact year. Unless this is a homework assignment, which need not reflect real life.  Edit - as indicated above, the first step is to get that value in 20 years:  The image is the user-friendly entry screen for the PV calculation. It walks you though the need to enter rate as per period, therefore I enter .1/12 as the rate. The payment you desire is $50K/yr, and since it's a payment, it's a negative number. The equation in excel that results is: =PV(0.1/12,240,-50000/12,0) and the sum calculated is $431,769 Next you wish to know the payments to make to arrive at this number:  In this case, you start at zero PV with a known FV calculated above, and known rate. This solves for the payment needed to get this number, $568.59 The excel equation is: =PMT(0.1/12,240,0,431769) Most people have access to excel or a public domain spreadsheet application (e.g. Openoffice). If you are often needing to perform such calculations, a business finance calculator is recommended. TI used to make a model BA-35 finance calculator, no longer in production, still on eBay, used.  One more update- these equations whether in excel or a calculator are geared toward per period interest, i.e. when you state 10%, they assume a monthly 10/12%. With that said, you required a 20 year deposit period and 20 year withdrawal period. We know you wish to take out $4166.67 per month. The equation to calculate deposit required becomes - 4166.67/(1.00833333)^240= 568.59  HA! Exact same answer, far less work. To be clear, this works only because you required 240 deposits to produce 240 withdrawals in the future. There's no standard formula. You can compare the going rates on the market for unsecured LOCs and take that as the starting anchor. Unsecured lines of credit run in the US at about 8-18%. Your risk should be reflected in the rate, and I see no reason why the rate would change throughout the loan. As to the amount of principal changing? Just chose one of the standard compounding options - daily (most precise, but most tedious to calculate), monthly average balance, etc. It would help if we had numbers to walk you through the analysis. Current balance, rate, remaining term, and the new mortgage details.  To echo and elaborate on part of Ben's response, the most important thing is to not confuse cash flow with savings. If you have 15 years to go, and refinance to 30 years, at the rate rate, your payment drops by 1/3. Yet your rate is identical in this example.  The correct method is to take the new rate, plug it into a mortgage calculator or spreadsheet using the remaining months on the current mortgage, and see the change in payment. This savings is what you should divide into closing costs to calculate the breakeven. It's up to you whether to adjust your payments to keep the term the same after you close.  With respect to keshlam, rules of thumb often fail. There are mortgages that build the closing costs into the rate. Not the amount loaned, the rate. This means that as rates dropped, moving from 5.25% to 5% made sense even though with closing costs there were 4.5% mortgages out there. Because rates were still falling, and I finally moved to a 3.5% loan. At the time I was serial refinancing, the bank said I could return to them after a year if rates were still lower. In my opinion, we are at a bottom, and the biggest question you need to answer is whether you'll remain in the house past your own breakeven time. Last - with personal finance focusing on personal, the analysis shouldn't ignore the rest of your balance sheet. Say you are paying $1500/mo with 15 years to go. Your budget is tight enough that you've chosen not to deposit to your 401(k). (assuming you are in the US or country with pretax retirement account options) In this case, holding rates constant, a shift to 30 years frees up about $500/mo. In a matched 401(k), your $6000/yr is doubled to $12K/year.  Of course, if the money would just go in the market unmatched, members here would correctly admonish me for suggesting a dangerous game, in effect borrowing via mortgage to invest in the market. The matched funds, however are tough to argue against. "Average return on the S&P500 over the last 10 years has been 1.6 %; so if you'd invested in that with money borrowed at 3 % you would have lost (so far). Investing with borrowed money implies you think you can beat the market: that you're a cleverer investor than whoever decided to lend you the money. Whoever decided to lend you the money decided that you are the best (return/risk ratio) investment for their money. It might make sense to invest borrowed money if you don't need to pay it back if things go wrong: if you're an investment professional whose bonus depends on the profit you make, but who won't need to repay any loss. It might also makes sense to borrow money if you're going to 'add value', e.g. sweat equity: for example if you use it to renovate a house or (if you're a business) to hire more staff. But the question was ""What guidelines do you use"" and the answer is, ""I don't make passive investments with borrowed money."" My Dad did it, i.e. didn't repay his mortgage as soon as he could have: but that was because (back in the '70s) he had a long-term (government-sponsored) mortgage for about 1.5 % (designed to help first-time buyers or something like that), at a time when banks were paying higher interest rates on (ultra-safe) deposits."