The population of Paris today is lower than its historical peak of 2.9 million in 1921. The principal reasons were a significant decline in household size, and a dramatic migration of residents to the suburbs between 1962 and 1975. Factors in the migration included de-industrialisation, high rent, the gentrification of many inner quarters, the transformation of living space into offices, and greater affluence among working families. The city's population loss came to a temporary halt at the beginning of the 21st century; the population increased from 2,125,246 in 1999 to 2,240,621 in 2012, before declining again slightly in 2017. It declined again in 2018.