California added 3.4 million people between 2000 and 2010, reaching a total population of 37.3 million. The latest estimate available for 2012 is 38 million. The state’s population is projected to reach 47.7 million in 2040.

California’s population growth has slowed from the high-growth decades of the 1970s and 1980s, when the rates were 18.7% and 26% respectively. Annual growth rates in California are expected to fluctuate between 0.9% and 0.8% until 2035.

There are two different estimates of California’s population, based on two different estimates of net domestic migration—the number of people moving to the state from elsewhere in the U.S minus the number of people leaving the state. The California Department of Finance’s population estimate is used by state agencies for programing and planning. The Census Bureau’s estimate is used nationally and for some allocations of federal funds.

Between 2011 and 2012 California’s population grew 0.95%. Growth varied widely across California: 19 counties, most of them in the northern part of the state, registered declines. Declines were greatest in Lassen County and Modoc County (both were down 1.8%).

The most populous counties showed growth rates above the state average; Los Angeles County was an exception, with a growth rate of 0.75%. Four counties in the Bay Area (Alameda, San Francisco, Santa Clara, and San Mateo) registered the highest population growth among California counties (between 1.5% and 1.4%).

Between 2011 and 2012 California added 255,853 people. The state gained 96,463 people due to net foreign immigration but lost about 110,000 people due to net domestic migration (more people leaving than moving to California). This resulted in a net migration loss of 13,526 people. Natural increase—births minus deaths—made up for this loss and then some, adding 269,379 people. California's net domestic migration has been negative for most of the last two decades.