What would this money be worth if I invested it instead?
Every spending decision has a hidden cost: the growth you forgo. See it in real and nominal dollars, both 10 and 30 years out.
How the math works
Two formulas, applied side by side. For one-time spending, future value is just FV = P(1+r)n
— what the dollars would have been in n years at rate r. For recurring spending, future value is the annuity formula FV = PMT × ((1+r)n−1) ÷ r,
compounded monthly.
We always show the inflation-adjusted version too. A $1M nominal account in 30 years isn't $1M of buying power; at 2.5% inflation it's closer to $478K. The "real" column tells you what the money would actually purchase, which is the only number that matters for decisions.
Default rate: 7% (long-run real S&P 500 average). Default inflation: 2.5%. Both are sliders. Lower the rate to 4-5% if you want to stress-test against a more conservative portfolio mix.
Math runs locally. Inputs never leave your browser. Source on github.
Scenarios we've already crunched
Common spending patterns run through the calculator, with the math worked out:
- Why the latte factor is wrong (and what is actually expensive) — $5/day on coffee = $184K over 30 years. A $400 too-much car payment = $487K. The ratio explains why structural decisions dwarf daily ones.
- A $35K new car's real cost is $850/month over 5 years — payment + insurance + depreciation + fuel + maintenance. Compounded over 30 years that's $1.02M not invested.
- When a side hustle is making you poorer — $500/month sounds great until you back out hours, expenses, and self-employment tax. Some hustles pay below minimum wage in real terms.
- Opportunity cost without the guilt trip — how to apply this framework to recurring decisions over $50/month, and ignore it for everything else.