Investment CalculatorFree online financial calculator — instant results, no sign-up
Project an investment with monthly contributions.
Estimates only, based on the inputs and assumptions shown. This is not financial, investment, tax, or legal advice. Prices, rates and local rules may change; crypto scenarios do not predict returns. Confirm important decisions with a qualified professional.
Sign in to save results and favorites.
How the result changes with starting amount
Each row below was calculated with this tool, keeping every other input at its default and changing only starting amount from half to one and a half times the default value. Use it to see how sensitive the answer is before you enter your own numbers.
| Starting amount ($) | End balance | Contributions | Growth |
|---|---|---|---|
| 10,000 | $300,850.72 | $130,000.00 | $170,850.72 |
| 15,000 | $321,044.41 | $135,000.00 | $186,044.41 |
| 20,000 (default) | $341,238.11 | $140,000.00 | $201,238.11 |
| 25,000 | $361,431.80 | $145,000.00 | $216,431.80 |
| 30,000 | $381,625.50 | $150,000.00 | $231,625.50 |
About the Investment Calculator
This calculator estimates the future value of an investment portfolio combining an initial starting sum with regular monthly deposits. It projects total account balance, cumulative capital contributed, and investment growth over a chosen holding period based on a constant annual return.
- Starting amount
- The initial sum deposited at year zero, in dollars (typically $0 or greater).
- Monthly contribution
- The recurring amount added at the end of every month, in dollars (typically $0 or greater).
- Return rate
- The expected annual nominal rate of return, in percent (for example, 7 for 7%).
- Years
- The total duration of the investment horizon, in years (positive whole or decimal number).
Formula and method
End balance = P × (1 + r)^n + C × [((1 + r)^n − 1) / r] Contributions = P + (C × n) Growth = End balance − Contributions
- PStarting amount (initial principal)
- CMonthly contribution
- rMonthly interest rate, calculated as Return rate / 1200
- nTotal compounding periods in months, calculated as Years × 12
The calculator converts the annual return rate and years into monthly periods (r = rate / 1200 and n = years × 12). It computes the compound growth of the initial balance and the future value of an ordinary annuity for the monthly contributions, summing both components before rounding to two decimal places.
Worked example
These are the calculator's starting values and the results it actually produces for them.
Inputs
- Starting amount20000 $
- Monthly contribution500 $
- Return rate7 %
- Years20 years
Results
- End balance$341,238.11
- Contributions$140,000.00
- Growth$201,238.11
How to use the Investment Calculator
- 1Divide the annual return rate by 1,200 to find the monthly rate r, and multiply years by 12 to determine total months n.
- 2Calculate the future value of the initial lump sum using P × (1 + r)^n.
- 3Calculate the accumulated value of the monthly contributions using C × [((1 + r)^n − 1) / r] and add it to the lump sum to get the End balance.
- 4Multiply the monthly deposit by n, add the initial principal to determine total Contributions, and subtract that total from the End balance to find total Growth.
Reading your result
The End balance shows the projected total portfolio size at the end of the investment horizon. Comparing Contributions against Growth indicates how much of your final balance stems from your own out-of-pocket deposits versus compound earnings.
Limitations
This model assumes a fixed annual return compounded monthly and does not account for market volatility, sequence of returns risk, taxes, management fees, or purchasing power erosion caused by inflation.
Common questions
Are contributions treated as occurring at the beginning or end of the month?+
The formula treats deposits as end-of-month payments (ordinary annuity), meaning each monthly deposit earns interest starting the month after it is deposited.
Does this calculation adjust for inflation?+
No, calculations use nominal rates. To model real purchasing power, you can enter an inflation-adjusted return rate (for example, a 7% nominal return minus 2.5% expected inflation equals a 4.5% real return).
Can I use a 0% return rate or negative returns?+
At a 0% return rate, your end balance simply equals your total contributions because no interest is generated. The formula can accept negative percentages, reflecting portfolio drawdowns.
Does the calculator save my information?+
Calculations run in your browser. While signed in, inputs and results are automatically recorded in account history; saving a result creates a separate saved record.
Further reading
You might also like
Interest Calculator
Growth of savings with compound interest and regular deposits.
Finance Calculator
Solve for future value from present value, rate, periods and payment.
Compound Interest Calculator
Compare compounding frequencies and see the effective rate.
Interest Rate Calculator
Find the rate on a loan from amount, payment and term.
Savings Calculator
How savings grow with deposits, interest and tax.
Simple Interest Calculator
Interest earned without compounding.
Results are estimates for informational purposes and are not financial, medical or legal advice.