Investment Calculator
Project an investment portfolio with monthly contributions, annual increases and platform fees — and see what the fees actually cost you.
How to use this calculator
- 1Enter what you have now and what you add each month.
- 2Set an expected return. Long-run global equity averages sit around 7–8% nominal, but any single decade can be far from that.
- 3Enter your actual fund and platform fees — the difference between 0.2% and 1.2% over 25 years is large.
- 4Read both the headline value and the "in today’s money" figure. The second one is the meaningful one.
How the calculation works
Bₘ = Bₘ₋₁ × (1 + (r − f)/12) + PMT- Bₘ
- Balance at the end of month m
- r
- Expected annual return as a decimal
- f
- Annual fee as a decimal, subtracted from the return
- PMT
- Monthly contribution, increased once a year if set
The balance is simulated month by month rather than solved in closed form, because an annually increasing contribution is not a level annuity.
Fees are modelled as a reduction in the return rate — the standard approximation for a percentage-of-assets charge.
The real (inflation-adjusted) value divides the final balance by (1 + inflation)^years.
Worked example
$10,000 plus $500 a month for 25 years at 7%, 0.4% fees
- 1.The net return is 7% − 0.4% = 6.6% a year, or 0.55% a month.
- 2.Contributions total $10,000 + (500 × 300) = $160,000.
- 3.Simulating 300 months gives a final balance of about $427,000.
- 4.Growth is therefore roughly $267,000, and at 2.5% inflation that balance buys about $230,000 of today’s goods.
Result: About $427,000 — roughly $230,000 in today’s money
What investing actually is
Investing means putting money into an asset in exchange for a claim on what it produces later — a share of a company’s future profits, the interest on a loan you effectively make to a government or corporation, or the rent a property generates. That is the dividing line between investing and saving: a savings account trades growth for safety and instant access, while an investment accepts some risk of loss in exchange for a return that, over long enough periods, has historically outpaced inflation by a meaningful margin.
That return arrives in two forms — the asset becoming worth more (price appreciation) and cash it pays out along the way (dividends or interest). Reinvesting the second kind rather than spending it is often the larger share of a long-term balance, which is exactly why this calculator compounds contributions and growth together rather than treating them as separate pots.
The building blocks of a portfolio
Almost every investment held by an individual falls into a small number of categories, each with a different risk and return profile.
- Stocks (equities) — an ownership stake in a company. Value rises and falls with the business’s prospects and with broader market sentiment — the highest long-run average returns among mainstream assets, alongside the most volatility.
- Bonds (fixed income) — effectively a loan to a government or company, repaid with interest on a schedule. Generally steadier than stocks, with returns capped by the agreed rate rather than open-ended.
- Funds — index funds, ETFs and mutual funds — pooled vehicles that hold many underlying securities at once, so a single purchase buys instant diversification. This is how most contributions in this calculator are typically invested in practice, rather than picking individual companies.
- Cash and cash equivalents — savings accounts, money-market funds and short-term deposits. Low risk of loss, but returns rarely keep pace with inflation over long stretches.
- Real assets — property, commodities and similar physical holdings, often included for the way they behave differently from paper assets during certain economic conditions.
Why time does more work than timing
Compounding means growth earns its own growth: the return in year two is calculated on the original balance plus everything year one added, and so on. Because that effect multiplies rather than adds, most of the total growth in a long projection is generated in the final years, even though the contributions themselves are spread evenly across the whole period.
The practical consequence is that starting early usually matters more than finding a marginally better return later. A contribution made in year one has decades to compound; the same contribution made in year twenty has only a few years left to do the same work, no matter how it is invested.
What fees quietly cost you
Fees are charged as a slice of the balance each year, which means they compound against you in exactly the way returns compound for you — a fee is not a one-off cost, it is a permanent drag on every future year’s growth as well.
- Expense ratio — the annual charge built into a fund’s price, quoted as a percentage of assets. Index funds typically charge far less than actively managed ones for a comparable asset class.
- Platform or account fee — charged by the broker or platform holding the investment, separate from anything the underlying fund charges.
- Advisory fee — charged by a financial adviser managing the portfolio on your behalf, usually the largest single cost if one is used.
- Transaction costs — trading spreads and commissions, which matter more for frequent trading than for a buy-and-hold contribution schedule.
Managing risk without avoiding it
Because a higher expected return generally comes with more volatility along the way, the practical goal is not to eliminate risk but to take a level appropriate to the time horizon and to smooth out the experience of investing.
- 1Diversify — spread money across many holdings and asset types so no single company or sector failure does lasting damage.
- 2Invest on a schedule — contributing a fixed amount at regular intervals — sometimes called dollar-cost averaging — buys more units when prices are low and fewer when they are high, without requiring any prediction of which is which.
- 3Match risk to horizon — money needed within a few years generally carries less risk than money that will not be touched for decades, which can absorb a downturn and recover.
- 4Rebalance periodically — bringing a portfolio back to its intended mix after markets have pushed it off balance keeps the risk level from drifting further than intended.
What this assumes, and where it stops
Assumptions
- Returns are constant and applied monthly. Real markets deliver the same average through a very different path.
- Contributions are made at the end of each month and never missed.
- Fees are charged as a constant percentage of assets and reduce the return directly.
- No tax is deducted. Results represent a tax-sheltered account unless you lower the return to compensate.
Limitations
- This is not a forecast. Sequence-of-returns risk means two portfolios with the same average return can end up far apart, especially if you withdraw during the period.
- It does not model asset allocation, rebalancing, dividends taxed differently from gains, or currency effects.
- Contribution limits on tax-advantaged accounts are not enforced.
Common questions
What return rate should I use?
There is no correct answer, only defensible ones. A globally diversified equity portfolio has historically returned roughly 7–8% a year nominally over multi-decade periods; a balanced portfolio less. Run the projection at several rates — the spread between 5% and 8% tells you more than any single number.
Do fees really matter that much?
Yes, and the effect is non-linear. A fee reduces your return every year, and the compounding you lose compounds too. Over 25 years, moving from 1.0% to 0.2% in charges typically increases the final balance by around 20%. Enter both and compare.
Should I look at the nominal or the inflation-adjusted figure?
The inflation-adjusted one, almost always. A projected balance of $1m in 30 years sounds transformative, but at 2.5% inflation it buys what about $477,000 buys today. Plan against purchasing power, not the headline number.
Sources
- The impact of fees on investment returns — US Securities and Exchange Commission
Formula and content last reviewed on .
Results are estimates for information only, not professional advice.
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