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.