For example, let's say you borrowed a $10,000 loan at 5% to pay for a 10-year bond with a 3% coupon rate. Once the bond is in high enough demand, you might resell it for $15,000 during your second year of ownership, more than beating the gap between the interest rate and coupon rate.
Real estate, as mentioned, is a common place to find negative carry. There are so many different ways that real estate can be profitable beyond simple expense-versus-income calculations. Writing off specific expenses can lower your tax burden, and you may gain considerable equity simply by owning the property for an extended period.
Foreign exchange trading (forex) is another common area in which negative carry is employed frequently. If you invest in a currency with a higher interest rate than the one you're borrowing in, time, geopolitics, and the mysteries of the currency markets can flip that investment into one that's significantly profitable once you cash out the invested currency and repay the loan.
Banking history and negative carry
Although it's much less common now, banks are sometimes deeply involved in negative carry territory. This happened in the early 1980s when mortgage interest rates were sky-high. It wasn't uncommon for those banks to issue mortgage loans at less than they were paying on six-month certificates of deposit (CDs).