Why Borrowing to Buy a Home Can Be Dangerous — DSR Rules and Japan's Lost Decades

People in Seoul have been lining up outside bank branches before dawn. They're racing to lock in favorable mortgage rates before interest rates rise or lending rules tighten — a phenomenon locals now call the 'loan open run.' It's not just a quirky trend. It's a sign of how heavily Korean households lean on debt to buy homes.

So, What Exactly Is DSR?

DSR stands for Debt Service Ratio — the percentage of your annual income eaten up by loan repayments (both principal and interest, across all your debts). Say you earn ₩50 million a year and owe ₩20 million in combined annual repayments. Your DSR is 40%. In Korea, once that number crosses the regulatory ceiling, banks are required to turn you down — no matter how badly you want that apartment.

Japan Skipped This Step — and Paid Dearly

In the 1980s, Japan's property market was on fire. Banks handed out mortgages almost regardless of income, and buyers piled in, convinced prices would never stop rising. Then, in 1990, the bubble burst. Property values collapsed — in some areas by more than half — but the debts remained full size. Defaults surged, banks crumbled, and Japan's economy fell into a slump that dragged on for over 30 years. That era is now called Japan's Lost Decades.

What Tighter DSR Rules Mean for Investors

When Korea tightens its DSR ceiling, borrowing capacity shrinks — which means fewer people can afford to buy. Less demand tends to cool price growth. That ripple reaches the stock market too. Homebuilders, real estate trust companies, and banks that rely heavily on mortgage lending all feel the pressure. A stricter regulatory environment is generally seen as a headwind for these sectors.