How to use this investment calculator
Enter initial principal, a fixed contribution per month, and a whole-month term from zero to 1200. Supply three effective annual return assumptions in ascending order, allowing negative rates down to −99%. Enter a percentage asset fee and inflation assumption, then select deposit timing. The scenario table shows gross and net model rates, while the checkpoint table follows the base scenario. All contributions use the selected currency label and remain fixed in nominal terms. No exchange-rate conversion occurs, and the tool does not obtain current market returns or account fees for you.
How the calculation works
An investment projection combines capital already present with money added over time. Unlike a deposit calculator focused on a contractual interest assumption, this page makes variation across three return assumptions visible and accepts negative returns. The scenario labels mean lower, base, and higher inputs only. They do not imply a statistically calculated pessimistic case, likely outcome, confidence interval, or worst-case loss. Real investments can perform outside the three selected scenarios.
The return input is an effective annual percentage before the entered asset fee. Each annual factor is combined with a fee factor: net annual growth factor = (1 + gross return)(1 − fee). The equivalent monthly factor is the twelfth root of that result. A 6% gross return and 1% asset fee therefore give a net factor of 1.06 × 0.99 = 1.0494, or 4.94%, not exactly 5%. This is a defined illustration of fee treatment, not a reproduction of every provider's charging method.
Annual return and fee factors are smoothed into twelve equal monthly periods. Contributions are credited at the beginning or end of each modeled month and subsequently participate in the same monthly factor. Actual market returns fluctuate, and providers may charge fees on daily or quarterly balances. Sequence matters when money is added or withdrawn. A constant-factor path cannot reproduce a volatile history simply because its headline annual percentage looks similar.
Total contributed equals initial principal plus monthly contribution times the number of months. Gain or loss is ending balance minus that contribution total and can be negative. Contributions are not earnings. Even a portfolio that grows relative to its starting balance can have a loss relative to all money deposited. The tool does not clamp losses to zero or describe capital added from savings as investment performance.
Fee drag is the difference between a matching projection without the asset fee and the projection with it. This includes the downstream effect of forgone growth, so it is not the amount of fees actually billed. Both comparison paths retain the same principal, deposits, gross return, timing, and duration. Transaction costs, account charges in currency amounts, tax, and other costs are excluded rather than hidden inside this percentage calculation.
Ending purchasing power divides the final nominal balance by (1 + inflation)^(months/12). It expresses the ending amount in the starting period's currency units under constant inflation. It is not a real investment gain calculated against the unadjusted contribution total, because contributions occurred at different dates. Contributions remain fixed in nominal terms; the tool does not increase them with inflation or compute a retirement spending budget.
Formulas
Net annual and equivalent monthly factors
End-of-month future value
Gain and purchasing power
Worked examples
Separate additions from performance
At zero return and zero fee, 1,000 initially plus 100 at the end of each month for twelve months becomes 2,200. Total contributed is also 2,200, so gain is zero. A 1,200 increase from the initial balance represents the deposits, not a 120% investment return.
A negative-return illustration
With 10,000 initially, no later contributions, no fee, and an effective annual return of −10%, twelve model months end at 9,000. Gain is −1,000. The negative rate is supported because a realistic scenario tool should be able to illustrate loss without changing the meaning of the input or forcing the result to show positive earnings.
Fees and inflation without contributions
A 10,000 balance at 6% gross annual return with a 1% asset fee ends one year at 10,494 under this model. Without the fee it would be 10,600, so modeled fee drag is 106. With 2% inflation, ending purchasing power is 10,494/1.02 ≈ 10,288.24 in starting-period currency units.
Common uses
Explore assumption sensitivity
Compare three chosen return paths while keeping the savings budget unchanged. This makes the impact of input assumptions visible without asserting that the middle path is likely. Test a negative scenario when relevant and remember that a constant path cannot represent the sequence, volatility, or extreme outcomes of actual market returns.
Understand fee drag
Change only the percentage fee to isolate its modeled effect on a projected balance. The no-fee comparison retains all other inputs. Its difference includes growth no longer earned on amounts removed by the fee factor; it should not be presented as an invoice, expense ratio disclosure, or exact sum charged by a provider.
Separate nominal value from purchasing power
Compare the base final amount with its inflation-adjusted display to understand the units of a long-horizon illustration. This is a comparison of the ending balance's purchasing power, not a personal retirement plan or real ROI. Contributions remain nominal, so subtracting their unadjusted total from that purchasing-power output would mix dated amounts.
Accuracy and limitations
Effective annual growth and asset-fee factors are combined and converted to equivalent monthly factors. Full precision is retained through contributions and checkpoint balances, with money rounded only for display. Whole-month terms permit partial final years. Floating-point estimates are rejected if magnitudes exceed the supported range instead of showing infinity or a misleading result.
This deterministic illustration is not a Monte Carlo simulation, probability model, financial forecast, or product recommendation. Rates, fees, inflation, and contributions are constant. Taxes, leverage, irregular transactions, and trading costs are omitted. In real markets the order of returns matters, especially with cash movements, and a long horizon does not remove the possibility of loss.
Sources and methodology
These references support the formulas and financial concepts explained on this page. Product-specific rates, fees, and contract conventions still need to be checked with the provider.
Frequently asked questions
Are the three scenarios forecasts?
No. They are constant-return illustrations using your inputs, with no probabilities or guarantee that actual outcomes fall between them.
Can returns be negative?
Yes. Effective annual scenario returns can range from −99% to 100%. The supported range is a software boundary, not a claim about investment risk.
Is fee drag the sum of fees charged?
No. It measures the projected balance difference caused by the fee assumption and also reflects forgone growth.
Does the tool subtract fee percentage points?
It combines annual growth and fee factors multiplicatively, then converts the net factor to a monthly equivalent. This assumption is displayed explicitly.
Are contributions adjusted for inflation?
No. Monthly contributions stay fixed in nominal terms. Only the final balance is expressed in starting-period purchasing-power units.
Does this recommend an investment?
No. It does not evaluate suitability, product quality, tax treatment, or an individual's ability to bear losses.