Every recurring charge is also a recurring opportunity cost. The same dollars, invested instead of spent, would compound. This calculator shows the gap — over any time horizon, against any reasonable market return. Use it on us. Use it on every subscription you have.
The math is the standard future value of an ordinary annuity: FV = P × ((1+r)n − 1) / r — where P is the monthly payment, r is the monthly return rate (annual ÷ 12), and n is the number of months.
The default 7% return is the rough long-run S&P 500 real (post-inflation) average. Pre-inflation it's closer to 10%, but real-return numbers are what you actually live on. The opportunity-cost number assumes you would have invested in a broad index fund, not picked individual stocks.
This calculator is also a checkbox-honest argument against our own subscription if you don't get value. The $9.99/mo Basic tier costs ~$36k in opportunity over 30 years at 7%. If Dragonfly doesn't help you beat that, don't subscribe. The point of the Lens is to give you the tools to evaluate every claim — including ours.
This calculator works on any subscription, not just ours. Run Netflix, Spotify, and your gym membership through it. Many monthly subscriptions cost more in opportunity-compounded dollars over a working lifetime than a used car. Most pricing pages won't show you this math because it isn't flattering to them. Ours does.
Of course, some subscriptions earn their cost back — that's the test. A $9.99/mo research subscription that helps you find one good position over 30 years can easily justify the opportunity cost. A $15/mo streaming service that mostly plays in the background? That's the one to question first.