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What Banks Hide

What's the real cost of waiting to invest?

The growth curve Wall Street counts on you ignoring. See how compound interest works for — and against — you.

Your Investment

S&P 500 historical avg ~7% (inflation-adjusted)
30 years

Cost of Waiting

Compare what happens if you delay starting by a few years.

3 years
5 years

Future Value

$691,150

$190,000

contributed

$501,150

free money

3.64x

multiplier

Your Money vs Compound Growth

The green area is "free money" - earnings from compound interest.

The Cost of Waiting

Every year you wait costs more than the last - that's compound interest working against you.

Start in 3 years
Final value$544,384
Cost of waiting-$146,766
Growth multiplier3.17x
Start in 5 years
Final value$462,290
Cost of waiting-$228,860
Growth multiplier2.89x

By investing $500/mo for 30 years at 7%, you'll contribute $190,000 but end up with $691,150. That's $501,150 in free money from compound interest. Waiting just 3 years to start costs you $146,766.

Compound Interest Calculator
whatbankshide.com
Future Value
$691,150
Total contributions$190,000
Total growth$501,150
Growth multiplier3.64x
Time horizon30 years at 7%

How It Works

This calculator applies your expected annual return rate on a monthly basis, adding your monthly contribution each period. The future value formula for regular contributions is: FV = P(1+r)^n + PMT × [(1+r)^n - 1] / r, where r is the monthly rate.

The key insight: The gap between your contributions (what you put in) and the final value (what you get out) is "free money" from compound growth. Over 30 years at 7%, a typical growth multiplier is 2.5-3.5×, meaning the market more than doubles your contributions.

The "cost of waiting" comparison shows how delaying even a few years dramatically reduces your final value, because those early contributions lose the most compounding time.

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Frequently Asked Questions

What is compound interest?
Compound interest is earning interest on your interest. When your investments grow, that growth itself earns returns the following year, creating an exponential snowball effect. For example, $10,000 growing at 7% earns $700 in year one, but by year twenty the annual gain is roughly $2,700 - even without adding a single dollar. Over long periods, compound growth dwarfs your actual contributions, often producing 2-3x or more of your total invested amount. Learn the quick Rule of 72 shortcut at /guides/rule-of-72.
Is 7% a realistic return rate?
The S&P 500 has returned roughly 10% annually before inflation, or about 7% after inflation, over the past century. Individual years vary wildly (-37% to +54%), but over 20-30 year periods, the average has been remarkably consistent. We use 7% as a reasonable long-term planning assumption.
Why does waiting a few years cost so much?
Because the money you invest earliest has the most time to compound. Your first dollar invested has the maximum time to grow exponentially. Waiting 5 years doesn't just lose 5 years of contributions - it loses the compound growth those early contributions would have generated.
Does this account for inflation?
If you use an inflation-adjusted return rate (e.g., 7% instead of 10%), then all values are in today's purchasing power, which makes it easier to understand what your future balance will actually be worth. If you use a nominal rate (10%), the final number is in future dollars, which will buy less than today's dollars. Historically, U.S. inflation has averaged about 3% per year. For most long-term planning, using a 7% real return for stocks is a reasonable default.
How do taxes affect compound growth?
In tax-advantaged accounts (Roth IRA, 401k), your money compounds tax-free, matching this calculator's output. In taxable accounts, annual taxes on dividends and capital gains reduce effective returns by 1-2%, so adjust your expected return accordingly.