The average income slipped from $55,714 in 2000 to $55,238 in 2005, after adjustment for inflation, according to analysis of IRS data by the New York Times.
While wages were rising in those years, they weren't able to keep pace with the growth in consumer prices for the average American worker.
The IRS data showed that while total income rose from 2000 to 2005, the growth was concentrated among those earning $1 million or more. Two-thirds of American reported incomes of less than $50,000 during that time period, the newspaper notes.
The White House told the newspaper that the reason the average income fell from 2000 to 2005 was that the country was still recovering from the "bubble economy" that began in the late 1990s.