Should I buy it or keep paying monthly?
Total cost of ownership vs total cost of subscription, with the opportunity cost on the upfront amount baked in. The break-even month tells you when each path wins.
How the math works
Two paths run in parallel against the same monthly horizon.
Buy path: upfront purchase price + maintenance per year + replacement cost at end-of-life. Resale value at sale time recovers a fraction. Importantly, the cash spent upfront could have earned the expected return — so the buy path includes opportunity cost: the future value the upfront amount would have reached at rate r.
Subscribe path: monthly fee compounded with annual price growth (subscriptions rarely stay flat). The cash freed up by not buying is invested at rate r, partially offsetting the subscription expense.
Break-even month is where total subscription cost (less invested savings) crosses total ownership cost (less resale, plus opportunity cost). Before that month, subscribe wins; after it, buy wins.
Math runs locally. Inputs never leave your browser. Source on github.
Real-world scenarios
- The break-even framework: when each path wins — $500 upfront vs $15/month + opportunity cost. The naive 33-month break-even shifts when you include the cost of capital.
- $200/month in subscriptions = $104K of forgone wealth over 20 years — how forgotten free trials and price creep silently compound against you.