Michael West Financials LLC · Est. 2024
Calculator · Investing

$200 a month, 40 years, and the magic of compounding.

Long horizons turn small monthly contributions into outsized balances — because growth earns growth. Punch in your numbers and see how much of the final pile is your money vs. compound interest doing its work.

Background Read the investment vehicles guide
Sample numbers below — edit any field to make them yours.
What do you want to find?
What you save into this account every month. Steady beats heroic — even $50 makes the chart curve.
$
How long the money has to grow. The last decade does most of the work.
years
7% is a common long-run estimate for stocks before inflation; tick "Show in today's dollars" below for the inflation-adjusted view. Markets vary; any single decade can be lower.
% / yr
If you already have money invested, put it here. Otherwise leave at 0.
$
$200/mo for 40 years at 7% — see how much is contributions vs. growth.
Compare scenarios +$10/mo · wait 10 yrs · nominal $
A small bump compounds into a big gap at long horizons. Even $10/mo adds up.
$ / mo more
Cost-of-waiting test. The years you skip at the start would have compounded the longest.
years to start
% / yr
Saved locally

The first decade does almost no work; the last decade does most of it. Time, not amount, is the input that matters.

You put in —
Growth on top —
Final balance · 40 yrs @ 7%
—
Your contributions + compounding growth
Adding $10/mo more would grow this to — — an extra — over 40 yrs.
Waiting 10 yrs to start would shrink it to — — that's — you'd never get back.
Waiting 10 yrs to start would raise this to —/mo — that's —/mo more, every month, for less time.
Enter a contribution and time horizon to see how it grows.
Your starting balance alone grows past this target — no monthly contribution needed. You're already coasting.
Show the math the formula, with your numbers
Watch the substitution

Estimates only. Monthly contributions, monthly compounding, constant return. Real markets vary year to year; assumed return is a long-run average, not a guarantee. Toggle "today's dollars" to see purchasing power — $1M in 40 years buys roughly $307K of today's groceries at 3% inflation.

01 · Your balance over time

The honest shape of a projection.

Your own numbers, drawn as the band of outcomes they really are — with what you put in below.

02 · Time × contributions

Most of the final pile is growth.

See how slowly growth catches contributions — then how fast it laps them.

The power of compounding

The first $100K takes — The last takes —

Investing $10,000/yr at a steady 7%, each $100K milestone arrives faster than the previous. Adjust the dials and watch the bar redistribute.

Source: contribution spread evenly across 12 months, monthly compounding at r/12, constant return.
Annual contribution $10,000
Annual return 7%
—
of the total time is spent reaching the first $100K.
—
of the total time is spent reaching the first $300K. The remaining $700K arrives in just — of the time.
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03 · Per-dollar leverage

$1 today vs. $1 a decade late.

Same compounding, framed per dollar — to make the cost of waiting impossible to look away from.

Wealth multiplier

Every $1 saved at 30 becomes — by age 65.

$1 invested at age 30 at a steady 10% becomes — by age 65. Every year of delay shrinks that number — and the cliff is steeper than most people think.

Source: monthly compounding at r/12. The band is a modeled range (annual returns treated as variable, σ ≈ 15%), illustrative — not a Monte Carlo run.

$1 today becomesat age 65
—
started at 30 · 10% / yr
Your age now 30
Annual return 10%
Inflation
% / yr
$ at 65 Age you start saving
Expected path The likely half (1 in 2) The wider range (8 in 10)
—
if you start at age 25.
—
if you wait until age 45 — a 20-year delay cuts the multiplier by roughly —.
By starting age · at — / yr

What $1 becomes — and what you'd have to put away monthly to land on $1M by age 65 . Drag the annual return slider above to recalculate.

Start age $1 today → Monthly to $1M

Lump sum, constant return, no taxes or fees. The same math drives compound interest everywhere — but framed per-dollar, the cost of delay is harder to ignore.

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How to read it

Most of the final pile is compound growth, not contributions.

With a 40-year horizon and a 7% return, roughly 80% of your final balance is what your money earned — only about 20% is the paycheck dollars you actually put in. Time is the biggest lever you have, and unlike income or returns, it doesn't require a raise or a bull market. It just requires starting.

Plain English

Compound interest means your earnings start earning earnings of their own. It looks underwhelming for the first decade, then accelerates.

The cost of waiting

Starting late is expensive.

Try setting "wait" to 10 years with the same monthly contribution and return. The shortfall isn't 10 years' worth of contributions — it's much bigger. The dollars you would have put in early had the most time to compound, so they're the most valuable dollars in the whole pile.

  • Years 1–10 contributions look almost flat against growth — boring, easy to dismiss.
  • Years 11–25 growth catches up and starts to dominate the bar.
  • Years 26+ growth lapping contributions multiple times. This is the part you can't replicate later.
Caveats

Where this estimate is rough.
  • Constant return. Real markets bounce around. 7% is a long-run average for diversified equities, not a yearly guarantee.
  • No taxes or fees. Roth accounts (Roth IRA, Roth 401(k)) and the HSA (for qualified medical) preserve the growth tax-free. Traditional 401(k)/IRA defers tax — the growth is taxed eventually as ordinary income on withdrawal. Taxable brokerage accounts lose some to taxes each year.
  • No inflation adjustment. A dollar in 40 years buys less than a dollar today. The numbers shown are nominal, not real.
  • Contributions held flat. Most people contribute more as their income grows; the calculator doesn't model that.
Next read

Make compounding work harder.

The calculator assumes you're already saving. The 401(k) and IRA guides cover where to put those contributions so the growth isn't taxed away.

Read the 401(k) guide → Read the IRA guide
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