Opportunity Cost is the invisible price you pay when you make a financial choice. When you spend money on a consumer item, that exact same money loses its ability to generate compound interest for you in the stock market or a savings account.
1. How to use this calculator
Check the "Single time purchase" option for one-off expenses, such as a vacation trip or an expensive gadget you are buying just once. For recurring costs, leave it unchecked and set the frequency: use this mode for both monthly subscriptions and items you will replace multiple times throughout your lifetime (like upgrading phones or laptops every few years).
2. Finding the Hidden Cost
A $15/month subscription feels like a minor expense. However, if invested at 4% real return annually for 10 years, that small recurring flow grows significantly over time. The gap between what left your pocket and what you could have built is your true opportunity cost.
3. Recurring Habits and Compound Drag
Small, repetitive purchases experience a "reverse" compounding effect. Upgrading your smartphone every two years or grabbing daily takeout are perfectly fine choices, but this calculator helps you quantify exactly how much future wealth you are exchanging for today's convenience.