The Saving Abroad at Low Interest While Borrowing at High Interest Dilemma: How Much of a Commodity Windfall Should a Middle-Income Country Save in Its Sovereign Wealth Fund? Empirical Evidence from Mongolia

Countries that sell raw materials like coal, copper, or oil face a unique financial tightrope. When global prices for these goods rise, the nation earns a sudden windfall of cash. At the same time, because the world sees the country as wealthier and more secure, banks and investors lend to it at lower interest rates. Conversely, when prices crash, the country's income vanishes, and lenders demand much higher interest to compensate for the increased risk. This double exposure creates a difficult choice for leaders: should they spend the extra money immediately to build roads and schools at home, or should they save it abroad in a sovereign wealth fund? The dilemma is sharpened by a specific reality in places like Mongolia: the government often has to borrow money at high interest rates to fund its operations, while the money sitting in its foreign savings account earns a much lower return. This creates a tempting argument to spend the savings now rather than let them sit idle, even though spending too much during a boom can lead to a painful crash when the prices eventually fall.

Researchers Tumendelger Lkhagvasuren and Batnasan Namsrai set out to solve this puzzle for Mongolia, a nation that recently joined the ranks of upper-middle-income countries and is currently debating how to manage its mineral wealth. They built a detailed computer simulation of the Mongolian economy to test different rules for handling these windfalls. The study moves beyond the two extreme positions often argued in public debate: either spending every dollar of extra revenue immediately or saving every single dollar abroad. Instead, the researchers asked a more practical question: what is the perfect balance between saving and spending to make the country as well-off as possible over the long term? To answer this, they first measured exactly how much Mongolia's borrowing costs change when commodity prices move. Using decades of data, they found that when commodity prices rise, the interest rate the government pays on its loans drops significantly, and when prices fall, the cost of borrowing spikes. They also confirmed that this relationship is not symmetrical; the cost of borrowing tends to rise much more sharply during a downturn than it falls during an upswing.

The simulation revealed that neither extreme is the right answer. Spending all the windfall money at home is risky because it fuels a credit boom that makes the economy vulnerable when prices drop. Saving everything abroad is also suboptimal because it misses the chance to invest in public infrastructure when the country is rich and borrowing is cheap. The model suggests a middle path is the most effective strategy. Depending on how sensitive the country's borrowing costs are to price changes, the best approach is to save roughly half to two-thirds of every windfall and invest the rest at home. This specific mix allows the country to build public capital when it is affordable while keeping enough cash in reserve to smooth out the inevitable downturns. The researchers found that Mongolia's current law, which directs 65 percent of extra mineral revenue into a sovereign wealth fund, sits very close to this optimal point. While the exact percentage might shift slightly based on different economic assumptions, the most important finding is that avoiding the extremes is far more critical than hitting a precise number.

The study also addressed a common objection: since the foreign fund earns a lower interest rate than the government pays on its debt, isn't it better to use the money to pay off debt or spend it at home? The researchers simulated a scenario where the fund earns a low rate while the government carries a high debt load. Even with this cost, the simulation showed that saving the majority of the windfall remains the best policy. The low return on the fund acts as a premium for insurance; it protects the country from having to borrow at crushing rates when a crisis hits. In fact, the model indicates that if the government can borrow cheaply during a bust, using the windfall to pay down debt is better than building a fund. However, if borrowing becomes prohibitively expensive when the economy struggles, the fund becomes a vital safety net. The researchers also tested a third option often seen in resource-rich nations: giving the windfall money directly to citizens as cash payments. Their results were clear: this approach is the worst possible rule. Handing the money to households during a boom amplifies the credit surge and leads to a deeper crash later, leaving the country worse off than if the money had been saved or invested in public projects.

Ultimately, the paper provides a clear roadmap for Mongolia and similar nations navigating the volatility of global commodity markets. The data suggests that the country should not swing between the poles of total spending and total saving. Instead, a steady strategy of saving about half to two-thirds of any unexpected income, while investing the remainder in public infrastructure, offers the highest long-term welfare. This approach acknowledges that while the foreign savings account may earn less than the government pays on its loans, the stability it provides against future borrowing shocks is worth the cost. The research confirms that the current legal framework in Mongolia is well-aligned with these findings, offering a robust path forward for managing the nation's resource wealth without falling victim to the boom-and-bust cycles that have plagued other commodity exporters.