Foregone Earnings

The difference in earnings or performance between what is actually achieved and what could have been achieved with the absence of specific fees, expenses or lost time. Forgone earnings represent the investment capital that the investor spent on investment fees. The assumption is that if the investor had been exposed to lower fees, he or she would have generated a better return. This term is often used when referring to management fees or other expenses paid to mutual funds, exchange-traded funds, or other pooled investment vehicles.

Investopedia says:

Foregone earnings as they relate to investment performance can be a big drag on the long-term growth of assets. Something as seemingly innocent as a front-end load or a 1% management fee can cost thousands of dollars as the years pile up, thanks to the wonders of compound returns. To limit forgone earnings, it is important to look at the costs associated with each investment. For example, say you have $10,000 to invest and one fund charges 0.5%, while the other fund charges 2%. If you invest in the 2% fund, you will be charged $200, while the 0.5% fund only charges $50. The difference, or $150, is your forgone earnings, which could have been invested instead of being lost to fees.

Investopedia: Foregone Earnings