Inflation and real returns

A $100 bill from 1990 still says $100. But it only buys about half of what it bought back then. The number on the bill never changed; what the bill can buy quietly did.

That's inflation. The number on the money stays the same while the prices of everything around it creep up. Over a single year, the change is small enough to miss. Over thirty years, it adds up to about half.

Nominal versus real

A bank account paying 2% a year sounds like the money is growing. The number in the account does grow — $10,000 becomes $10,200 after a year. That's the nominal rate: the number printed on the statement.

But if everything got 3% more expensive that same year, $10,200 now buys roughly what $9,903 bought a year ago. The dollar amount went up; what those dollars can buy went down. The real rate is what's left after subtracting inflation — in this case, about -1% real.

When this stage talks about a stock portfolio earning "about 7% a year," that's already the long-term real return — inflation is already subtracted. The dollars don't just grow in number; they grow in what they can buy.

What inflation does to cash over thirty years

Picture $10,000 set aside in 1994 and never touched. Three places it could sit:

• A savings account paying close to nothing in real terms — about 0% real
• A bond (a loan to a government or a company that pays interest back to the lender) — about 1% real on average
• A mix of many different stocks — about 7% real on average

After 30 years:

• The savings holder still has $10,000 in dollars — but those dollars buy roughly what $4,100 bought in 1994. About 59% of the buying power is gone.
• The bond holder mostly kept up with prices; the buying power held steady.
• The stock investor's $10,000 grew to roughly $76,000 in 1994's buying power — more than seven times the starting amount.

Why cash feels safe and isn't

The number in a savings account never goes down. No scary dips, no headlines about a 30% loss in a single month. The chart line is flat. But that flat line is hiding a slow drift — each year the dollars are still there; each year what they buy is a little smaller. Over one year, it's small enough to ignore. Over thirty, it isn't.

Stocks swing year to year. They lose value sometimes, and the headlines are loud when they do. But the long-term average comes out ahead of the slow drift of cash. The visible drops in stocks are easier to notice than the invisible drops in cash — but only one of the two tends to recover.

Two people, same $20,000

Drew parks $20,000 in a high-yield savings account paying 2% a year, planning to use it for a down payment in 25 years. Inflation averages 3% over that stretch. Drew's nominal balance grows — after 25 years it lands near $32,800 in dollars. But $32,800 in 25 years only buys what about $15,700 buys today. The plan kept the dollars; it lost buying power.

Quinn puts $20,000 in a mix of stocks for the same 25 years. At about 7% real, that $20,000 grows to roughly $108,000 in today's buying power. Same starting amount, very different ending capability.

The difference isn't about being smart or lucky. It's about which line the money sits on — the slow erosion of cash, or the upward curve of compounding stocks.

Use the calculator below to try the math. Plug in a starting amount, a nominal interest rate, an inflation rate, and a number of years. Watch how the dollar balance and the buying power split apart as the years pile up.