Until the 1960s, North Korea's economy grew much faster than South Korea's. Although North Korea was behind in total national output, it was ahead of South Korea in per capita national output, because of its smaller population relative to South Korea. For example, in 1960 North Korea's population was slightly over 10 million people, while South Korea's population was almost 25 million people. Annual economic growth rates of 30% and 21% during the Three-Year Plan of 1954–1956 and the Five-Year Plan of 1957–1960, respectively, were reported. After claiming early fulfillment of the Five-Year Plan in 1959, North Korea officially designated 1960 a "buffer year"—a year of adjustment to restore balances among sectors before the next plan became effective in 1961. Not surprisingly the same phenomenon recurred in subsequent plans. Because the Five-Year Plan was fulfilled early, it became a de facto four-year plan. Beginning in the early 1960s, however, North Korea's economic growth slowed until it was stagnant at the beginning of the 1990s.