Foursquare predicts Apple will sell 15M of the iPhone 6s and 6s Plus this weekend

Foursquare expects Apple will sell roughly 13-16 million iPhone 6s and 6s Plus phones this weekend based on foot traffic leading up to the launch.

That would be a big leap from last year, when Apple sold 10 million of the iPhone 6 and 6 Plus during opening weekend.

The app, which unearths shopping, eating, and entertainment destinations, is using its vast swathes of data about consumers and Apple stores to predict how many of the iPhone 6s will sell this weekend.

Here’s how it reached its conclusions:

Each time Apple launches a product, it sees a giant sales spike. To determine the degree to which sales will jump during the launch of the 6s phones, Foursquare looked at historical data comparing iPhone sales during a launch weekend with sales during the rest of the quarter.

Over the last three years, the difference between the average weekly sales and product launch weekends was roughly 200-300 percent, depending on the year.

It turns out that annual product-launch sales spikes roughly correspond to the increase in foot traffic that Apple’s stores see over the same period. During the iPhone 6 launch, for example, both foot traffic and sales experienced a 230 percent jump.

Already this week, Apple stores around the world are seeing 3.6 times the amount of foot traffic they do on average.

“That shows a level of enthusiasm that promises a better first weekend than we’ve seen in the past,” said Foursquare COO Jeff Glueck.

To collect foot traffic data, Foursquare taps into its 50 million monthly active users. The app turns on a background “awareness” feature when a person is in a location for more than five minutes, regardless of whether they have the Foursquare app open. Glueck assures me that all data collected is anonymized.

He also acknowledged that this metric doesn’t directly account for pre-orders online or phones sales through carrier stores. That said, the last few years indicate that foot traffic seems to be pretty closely related to sales. That means Apple is in for another banner year.