You can check out above graph to see how the market cap of Stellar has changed over time. The market cap value depends on the value of Stellar on that particular day and number of Stellar in supply at that day.

How is Stellar Market Cap calculated?

The Stellar Market cap is calculated using a simple formula. You can find it below:

Stellar Market Capitalization in USD = Number of XLM in supply X Price of one Stellar in USD

Since the price of Stellar is highly volatile you can see the market cap going up and down a lot. Sometimes price and market cap are not linear to each other due to increase in the supply of coins in the market and stable or decrease in the price of the coin. So you can say that it's not simple to predict the market cap of Stellar or predict the price of Stellar.