Investment Growth Calculator
Explore how your starting balance, monthly contributions and time could shape a future balance.
(including starting amount)
(excluding starting amount)
A scenario, not a guarantee. Assumes a constant monthly return equivalent to your annual input, with end-of-month contributions. Actual returns fluctuate, losses are possible, and results are not guaranteed. Figures are nominal; taxes, fees and inflation are excluded.
Balance over time
Year-by-year projection
| Year | Total contributed | Gain / loss | Balance |
|---|
Contributions include the starting amount. The balance and gain/loss reflect the entered constant-return scenario.
See what your contributions could become
An investment balance has two parts: the money you put in and the gain or loss that accumulates over time. This calculator separates those parts so a growing account is not mistaken for investment performance alone. Start with an existing balance, add a regular monthly contribution, then explore a time period and an assumed return.
The blue line follows the projected account balance. The dashed line shows the total you have contributed, including your starting amount. A balance below the contribution line represents a projected loss. The yearly table gives the same information in numbers, beginning with year 0.
How the projection works
The return you enter is an effective annual return. We convert it into an equivalent constant monthly return, then apply that return to the opening balance each month. Your contribution is added at the end of that month, so it starts earning or losing value in the following month.
Next balance = current balance × (1 + monthly return) + monthly contribution
Total contributed = starting amount + monthly contribution × number of months
Projected gain or loss = projected balance − total contributed
This is why the annual rate is not simply divided by 12. For example, a 12% effective annual return corresponds to about 0.9489% per month. With no contributions, 1,000 becomes 1,120 after one year in this model. A nominal annual rate compounded monthly uses a different convention.
When monthly contributions are zero, the result follows starting amount × (1 + annual return ÷ 100)years, matching the annual-growth convention of our Compound Interest Calculator. Calculations keep full available numeric precision between months; only displayed amounts are rounded to two decimal places. A row's displayed figures can differ by a cent when added because each is rounded separately.
Choose assumptions you can interpret
- Starting amount: the balance at the beginning. It is included in total contributed, even if your existing account already contains past gains or losses.
- Monthly contribution: the same new amount at every month-end. Enter 0 to model a single lump sum. Withdrawals and increasing contributions are not modeled.
- Years: a whole number from 0 to 100. Zero years shows only your starting point, without a contribution or return.
- Annual return: a hypothetical constant percentage. Try your own positive, zero and negative scenarios. The example is illustrative and is not a prediction or recommended return.
A quick example without investment gains
With a starting amount of 1,000, contributions of 100 per month and a 0% annual return for two years, the final balance is 3,400. You supplied all 3,400, so projected gain is zero. At a negative return, the final balance can be below your total contributions even while deposits keep the balance growing.
What this estimate leaves out
Real investments do not earn a smooth, fixed return each month. Prices and returns fluctuate, and the order of those returns affects results when money is added or withdrawn. This tool does not model volatility, probability, individual securities, market timing or whether a goal is likely to be reached. Losses are possible and no result is guaranteed.
Amounts are nominal: they are not adjusted for inflation. Taxes and investment fees are excluded. Inflation can reduce what a future balance buys, and costs can reduce the amount that remains invested. Use consistent currency units throughout; changing the display currency does not convert money or fetch exchange rates.
Common questions
What happens with a negative or −100% return?
A negative assumed return reduces the existing balance each month before a new contribution is added. At exactly −100% annually, the equivalent monthly return is also −100%: every month erases the prior balance. The contribution added at the end of the last month remains. This is an extreme mathematical boundary case, not a market forecast.
Are contributions made at the beginning or end of each month?
At the end. A beginning-of-month contribution would have one additional month of returns. A one-year projection here contains 12 contributions; the final one receives no return before the projection ends.
Can I use it for savings with a fixed rate?
You can model a constant effective annual rate as an illustration, but check the actual account's rate definition, deposit timing, fees and compounding rules. This calculator does not verify an account's terms. For a contribution-free estimate, use Compound Interest; to divide a target into regular deposits, see Savings Goal.
Why is an extreme scenario rejected?
Starting amounts and monthly contributions are limited to 1,000,000,000 each. The annual-return input accepts −100% to 1,000%, with up to 100 whole years. Projections above 1,000,000,000,000,000 are rejected to keep results readable and numerically useful. These are software limits, not realistic investment expectations. Very large outputs use standard floating-point arithmetic and may lose cent-level precision.
Learn more from official sources
Investor.gov's Compound Interest Calculator illustrates how time, deposits and interest assumptions affect growth; its selectable compounding convention may differ from this tool. Read the SEC's investor education pages on investment risk and understanding fees for important context. This is an educational estimate, not personalized investment advice.