How the numbers work
No black box. Here's exactly where the data comes from, how every figure on the site is calculated, and — just as important — what we leave out.
Where the data comes from
Asset prices are monthly closing values pulled from Twelve Data. Inflation is measured with the U.S. Consumer Price Index (series CPIAUCSL) published by the Federal Reserve Bank of St. Louis (FRED). We refresh the dataset periodically rather than quoting live intraday prices — this is a tool for the long arc of an investment, not a ticker.
A few assets are tracked through a close stand-in: broad indices use their large, liquid ETFs (the S&P 500 via SPY, the Nasdaq-100 via QQQ), and metals use their spot pairs (gold and silver in USD per ounce). Because every result here is a ratio — today's price divided by your start price — the difference in absolute level between an index and its ETF cancels out, so the multiple and the growth rate come out essentially the same.
What “since 2015” actually means
When you pick a year, we assume you invested at that year's year-end closing price (December 31) and held to the most recent data we have. Picking 2015 means “from the last trading day of 2015.” It's a single, consistent reference point that keeps every scenario comparable.
The three ways to invest
All at once (lump sum). Your money buys as many shares, coins, or ounces as the start-date price allows, and that fixed quantity is revalued at every later price. Simple and unforgiving — timing is everything.
A bit each year (dollar-cost averaging). You contribute the same amount every year from your start date onward. Each contribution buys at that moment's price, so you accumulate more units when prices are low and fewer when they're high — which usually smooths out the ride compared with betting everything on one entry point.
Skip the latte. You give us a small, recurring spend — a $5 daily coffee, a $2 soda — and we convert it into the equivalent monthly amount (a $5/day habit is about $152/month) and run it through the same dollar-cost-averaging engine, buying monthly. It's the “what if I'd invested it instead” framing, made literal.
How we calculate the “per year” return
For a lump sum, the annual growth rate is the plain compound annual growth rate (CAGR): the steady yearly rate that turns your start value into your end value over the holding period.
For anything with multiple contributions (dollar-cost averaging and the latte factor), a single CAGR would be misleading, because a dollar you invested last year hasn't had the same time to grow as one from a decade ago. So we compute a money-weighted return — the internal rate of return (the same idea spreadsheets call XIRR) — which accounts for the exact timing of every contribution. It answers “what annual rate did my actual stream of deposits earn?”
How the habit pages work
The habit pages take an everyday recurring spend — a weekly bet, a daily energy drink, a monthly subscription — and ask what it would be worth had you redirected that same money into the market instead. We convert the habit into a single equivalent monthly contribution (a $20-a-week habit becomes about $87 a month) and run it as a steady monthly investment from the start year to today, using the exact same engine and money-weighted return as the latte-factor mode above.
Two things we say plainly, because they matter. First, the framing: the asset did the growing — quitting the habit just freed the cash to do it. We're not claiming willpower compounds; the market did. Second, the model is deliberately clean. It assumes you actually invested every month without fail, and — like everywhere else on the site — it ignores taxes, fees, and the messy reality that real people skip contributions. So treat the headline as the upper-bound what-if, not a forecast. The across-assets rail on each page only includes assets with price data for the entire window, so nothing gets an unearned head start.
Today's dollars
Every result also shows the end value in today's dollars. A 2010 dollar bought more than a 2026 dollar does, so we deflate the nominal result by the change in CPI between your start date and the end date. It's the honest way to see how much your money actually grew, not just how the number got bigger as the currency shrank.
The story behind the number
Each scenario page also breaks down the journey, not just the destination — and every one of those figures is computed straight from the same price series, so it stays honest as the data updates.
Best and worst year are the calendar years inside your holding period with the largest and smallest year-over-year change in the asset's price. Steepest drop is the maximum drawdown: the biggest peak-to-trough fall in the value of your position at any point along the way, measured from the highest level it had reached. Where the value later climbed back above that old peak, we note the year it recovered.
The ride label — from “a remarkably smooth ride” to “a white-knuckle rollercoaster” — is a plain-English read of how volatile the annual returns were (their standard deviation). It describes the bumpiness of the path, not whether it ended up or down.
The comparison pits each asset against the most natural yardstick over the identical window: the S&P 500, the default benchmark for “I could have just bought the index instead.” The S&P 500's own pages are measured against gold, the classic play-it-safe alternative. Both sides start with the same amount on the same date, so the ratio is apples-to-apples.
What we leave out
To keep the model clean and comparable, it deliberately ignores several real-world frictions. Returns are price-only: they don't reinvest dividends, which understates the true total return of dividend-paying stocks and broad indices. We also don't model trading fees, bid-ask spreads, taxes on gains, or the practical difficulty of buying a fractional coin in 2011. Stock prices are split-adjusted so a share count stays consistent through any splits along the way. Real investing is messier — and usually a bit more expensive — than the clean line you see here.
Not financial advice
These are historical what-ifs for education and curiosity. Past performance never predicts future results, the assets shown include some of history's most volatile, and nothing here is investment, tax, or financial advice. Treat it as a thought experiment, not a recommendation.