In 2018, Switzerland's population slightly exceeded 8.5 million. In common with other developed countries, the Swiss population increased rapidly during the industrial era, quadrupling between 1800 and 1990 and has continued to grow. Like most of Europe, Switzerland faces an ageing population, albeit with consistent annual growth projected into 2035, due mostly to immigration and a fertility rate close to replacement level. Switzerland subsequently has one of the oldest populations in the world, with the average age of 42.5 years.