The demographics of visitors to a website or category of web sites can shift dramatically in a short period of time (Hat tip to Chris Hafer for pointing out the demo-shift in online tax filers). The chart below shows the pattern of visits to the Accountancy category (where all online tax sites live). We’ve seen this repeating pattern every year, with the first week of February marking the biggest spike of visits to the category (taxpayers have their W-2s by this time and are filing online, probably expecting a refund), and a second spike the second week of April, the last minute filers.

If we look at the demographics for these two spikes, we see the interplay between two economic incentives; 1) the incentive for lower income households to file early to get a refund as soon as possible, and 2) the incentive for higher income households to delay paying taxes as long as possible.

Of course there are other factors that works independently of the economic incentives probably the most common — procrastination.