December Data on Facebook’s US Growth by Age and Gender: Beyond 100 Million

Facebook has been steadily climbing towards 100 million monthly active users (MAU) in the United States, and it finally reached the milestone late this past month, according to the self-reported data in its advertising tool.

Here’s a closer look at how those numbers break down by age and gender. Be sure to check out the caveats for these numbers at the end of the article — the short of it is that you should take all of these numbers as estimates.

Overall, growth appears to have continued at around the same rate as before: Nearly 5 million users joined the site in December, pushing the total from 98.1 million MAU to nearly 103 million MAU. The previous two months saw increases of around 4 million apiece.

Women, especially younger women, continue to comprise the single largest demographic groups within the US. In total, women constitute over 56% of the overall Facebook population — a continuation of a long-time trend.

Younger users saw the biggest numerical increases in December and the 26-34 range saw the largest overall increase, adding 839,000 new MAU, most of whom were female. Earlier last year, we were seeing stronger relative growth in older demographics. Maybe Facebook is facing challenges retaining older users?

In terms of growth rates, younger people and older men saw the fastest growth, as you can see below, with women over 55 not joining the site as fast as they had been earlier last year. In December, men over 55 on Facebook grew over twice as fast as women over 55.

As we enter 2010, only 40% of Facebook users are under the age of 25 – 60% are 26 or older, and nearly 20% are 45 are older. While it started as a site for students in a few colleges, American use of Facebook today is very intergenerational.

Note that the total number of users in a given age group is higher than the combined number of males and females within it, and for a couple reasons. One is that not every user designates their gender on Facebook, either by choice or because they forgot to. Another reason is that overall demographic numbers are estimates.

And now for the caveats, as there are significant irregularities in this data. Facebook’s advertising tool typically reports traffic numbers around a month later than what the company sees internally, judging from what we have observed in the past. And, repeated sampling of any demographic within a single day will typically show a few variations for the numbers. For example, when we took a sample from the advertising tool on January 1 to compare against our sample in early December, we saw the following results for the total number of MAU in the US: nearly 103 million but also 99 and nearly 104 million. Problematically, these estimates appear to differ whenever one sorts the advertising tool for a specific demographic, meaning we don’t have a good window into whether or not each demographic is high or low. The best we can do, given the irregularities in the data, is to look at overall trends. So, don’t assume any of these numbers are facts, but rather loose estimates that are better than nothing.

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