Pack-a-day smoker over 20 years with invested alternative
A 45-year-old has smoked one pack a day for 20 years at an average price of $10 per pack. They want to see what they've already spent and what that money would be worth today had it been invested at a 7% average annual return instead.
ResultDirect lifetime spend = $10 × 365 × 20 = $73,000. Future value of $304/month invested for 20 years at 7% = roughly $156,000. Opportunity cost (the gap) is about $83,000 of foregone wealth.
Daily cost is one pack × $10 = $10, which multiplied by 365 gives an annual outlay of $3,650 and by 20 years gives $73,000 in raw cigarette spending. The investment side treats the same $304/month as deposits into an index fund earning 7%. The future-value-of-an-annuity formula compounds each monthly deposit for the months remaining, landing near $156,000. The difference between the two numbers is the opportunity cost — money that didn't just disappear, it never got the chance to grow.