If you haven’t already heard, Amazon is buying Whole Foods.

Amazon’s purchase of Whole Foods is its biggest buy yet. It’s also a deal that would never have been possible when Amazon went public 20 years ago. At the time, Amazon was worth $505 million, whereas high-end supermarket Whole Foods was valued at $824 million.

The two companies’ market capitalization remained somewhat comparable through Amazon’s first decade as a public company. Then, in 2009, Amazon’s value began to take off as the online retailer gobbled up market share from traditional brick and mortar retailers. These days, Whole Foods, with a market cap of $13.4 billion, looks like a bargain compared to Amazon, worth $475 billion.

Already today, Amazon’s market cap has increased $15 billion — it closed yesterday at $460 billion and is currently $475 billion — meaning it’s already paid for the $13.7 billion acquisition of Whole Foods.