Skip to content

Tools

Compound Interest Calculator

You are really here to answer one question: will this be enough? So this one does what most calculators don't. It turns your final balance into what it actually means: a monthly income for life, and how much of it you never had to earn.

Built by Philipp Misura — nearly two decades in the financial industry. No sign-up, no email, nothing to sell.
Shows your monthly income for life Optional 2% inflation view Honest about fees & tax

Only the currency changes — the return assumption is the same worldwide.

Portfolio growth over time, split into contributions and compound growth A stacked area chart showing how much of the final balance you contributed versus how much came from compound growth.
What you paid in What compounding paid you Hover the chart to read any year
$
$
30
7.0%

Broad global equity has historically returned roughly 7% a year in nominal terms over long periods. That average hides individual years as strong as +54% (S&P 500, 1933) and as brutal as −43% (1931) — and −37% as recently as 2008. An average, not a forecast.

Show the whole thing in today’s money — what the final figure will actually buy.

In 30 years, you'd have

$0

You paid in

$0

Compounding added

$0

The crossover

—

What that actually means

At a 4% withdrawal rate, that balance could pay you about $0 a month.

—

Where the 4% comes from: William Bengen's 1994 study, and the Trinity study that followed. Both tested US history and asked how much you could draw from a portfolio of roughly half shares, half government bonds — raising the amount each year with inflation — without running out. The answer was 4% of the starting balance, and it held for at least 30 years. That is a 30-year planning figure from one country's past, not a promise of income for life and not a guarantee the capital survives. Whether it holds for you comes down to two things: what you put in the account and keeping your nerve when markets fall.

Illustrative arithmetic at a constant rate, compounded monthly. Excludes tax, inflation, fees and sequence risk — the S&P 500 returned −18.1% in 2022, +26.3% in 2023 and +25.0% in 2024, not a steady 7%. Not financial advice.

Why the crossover is the whole point

Compounding is famously described as a snowball, which is a nice image and slightly misleading, because it suggests smooth and visible acceleration. What actually happens is that almost nothing seems to happen for a long time, and then the arithmetic quietly takes over.

There is a specific year in which the growth on your portfolio first exceeds everything you have ever contributed to it. Before that year, you are the engine. After it, your money is. Move the sliders above and watch where it lands.

This is why the single most valuable variable is not how much you invest. It is how early. Ten years of extra compounding at the end of a horizon is worth more than a decade of doubled contributions at the start, because those final years are operating on the largest balance you will ever have.

What this deliberately ignores

  • Sequence risk. Real markets do not deliver 7% every year. The S&P 500 returned −18.1% in 2022, then +26.3% in 2023, then +25.0% in 2024 (total return, dividends reinvested). Two paths can arrive at the same average and feel nothing alike, and once you are drawing an income the order those years arrive in changes what you are left with. See it play out across 30 real years →
  • Fees. They come straight off the return. A 1.5% fee turns a 7% assumption into 5.5%, and over 30 years that is not a rounding error. See what a fee actually costs over a lifetime →
  • Inflation and tax. Both reduce what the final number is actually worth to you. Check the real rate on your money →

None of that makes the exercise useless. It makes it a floor for your thinking, not a forecast of your future.

Before you trust that number

Three things the chart leaves out

The calculator shows steady, nominal growth. In the real world three forces quietly shrink that final figure, and none of them appear on the curve. Each takes about two minutes to check.

Costs

Fee Drag

A 1.5% fee can quietly remove a third of your final pot.

 Purchasing power

Inflation

Your balance grows. What it actually buys may not.

 Behaviour

Behaviour Gap

Your own timing can cost more than fees and inflation combined.
Read next: How to pick an ETF → Index vs active funds → The 3-bucket structure → Rent or buy? →
Watch the videos on YouTube →
Share this

Questions people actually ask

How does compound interest actually work?

You earn a return on your money, and then in the following period you earn a return on that return as well. The growth itself starts producing growth. Early on this is barely visible — the effect is almost entirely back-loaded. Over decades it becomes the dominant force in a portfolio: with $500 a month at 7% over 30 years, more than half the final balance is money you never contributed.

What is the crossover point in compound growth?

The crossover is the year in which the accumulated growth on your portfolio first exceeds everything you have contributed. Before it, you are doing most of the work. After it, your money is. On typical assumptions — regular monthly contributions at around 7% — the crossover tends to arrive somewhere in the second or third decade, which is precisely why starting early matters far more than starting with a large sum.

What return should I assume in a compound calculator?

There is no correct answer, only honest ranges. Broad global equity indices have historically delivered roughly 7-8% a year in NOMINAL terms over long periods — after inflation, closer to 5% real (Dimson, Marsh & Staunton, Global Investment Returns Yearbook). The ~7% real figure often quoted applies to US equities, not global ones. This calculator works in nominal terms. Anything above 10% as a long-run assumption is not a projection, it is a wish. Model a lower number and let reality surprise you upward.

Does this calculator adjust for inflation and tax?

For inflation, yes — flip the "Adjust for 2% inflation" toggle and the chart adds a lower "today's money" line, plus the real value of your final balance called out beneath the headline number. Tax is deliberately left out to keep the arithmetic transparent: it reduces what you keep, just as fees come off the top of your return. Use the fee calculator for the cost side.

Sources — retrieved August 2026

The 7% default is a rounded long-run nominal figure, not a measured average of any one index — treat it as a starting point and move it. The calculator runs constant-rate arithmetic: it deliberately excludes tax, fees and sequence risk, each of which has its own tool on this site.

What this tool is — and what it is not

Runs in your browser
Your numbers are never sent anywhere. There is no account, no sign-up and no server doing the maths. Analytics are cookieless and EU-hosted, and your IP address is not stored. The full privacy detail →
Nothing to sell
No course, no recommendation, no affiliate links, no ads. If that ever changes, it will say so here before it says so anywhere else.
Not financial advice
This is a model, not a personal recommendation. It does not know your tax position, your job security or how well you sleep. A decision this size belongs in a conversation with someone licensed to advise you.
Who built it
Philipp Misura — Nearly two decades in the financial industry — first inside the institutions, then advising them. More about Philipp →