The so-called opportunity cost refers to the cost of choosing one of them and giving up the other options. If your question refers to the opportunity cost of going to college, we can analyze it from the following angles.

1, time. The length of college education is four years. If you don't choose to go to college, you can do other things in these four years. Such as work, entrepreneurship and so on. The accumulated experience of work and entrepreneurship is the loss of interests. So in terms of time, your opportunity cost is four years.

2. Tuition. Four years' investment in a university is the opportunity cost. These funds can also be used for other investments. Like stocks.