<prompt> Human: It would be helpful if someone explained opportunity cost to me. People have referred to it in some of my previous posts but I dont really understand it. I just got my salary increase to 90K pretax. I have over 300K in student loan debt. I anticipate being able to make close to 130-150K in the future. As far as opportunity cost goes, people have referred to it when I mentioned my previous relationship. A lot of people stated she is better off making 70K pretax with limited income potential and having no debt, than me having a 90K salary with income earning potential with my debt load. We are both in our 30s but she hit close to the max of what she will make. I dont understand why everyone says this is better off. I realize I have a lot of loans to pay but I make a good salary.  <response>: take the 3000month you are spending on debt repayment and put it in a compound interest calculator like this one - at a very modest 5 annual rate of return, over 15 years you would have 800K instead of possibly finishing paying off your debt. Thats your opportunity cost. 