Question

what is the formula for opportunity cost

Answer 1

Opportunity cost is your most valuable alternative. For example; you could spend the day working for $10/hr for 8 hours, or doing $100 worth of yard work at your own home. If you decide to do the yard work, then the opportunity cost would be the $80 you would of made while working.

Answer 2

The formula to get the opportunity cost is basically what you gave up over what you gained.