Estimate how your investment could grow using a starting amount, regular contributions, and an assumed return rate, with a simple breakdown of what you put in versus what your money earned.
Advanced options
How to use our Investment Calculator
- Enter your starting amount (the money you invest today).
- Enter your contribution amount, then pick whether you contribute monthly or yearly.
- Enter the time horizon in years.
- Enter your estimated return rate (percent per year). This is your guess for average growth.
- Open Advanced options if you want to match real life more closely (compounding, contribute at start vs end, inflation, fees, taxes, and a low/high scenario).
- Click Calculate.
- Read the ending balance (future dollars) and compare it to Total contributed to see Total growth.
- If you entered inflation, also check the ending balance in today's dollars to understand purchasing power.
- Use the schedule table to see how contributions and growth add up over time (switch yearly vs monthly if needed).
Definitions
Starting amount: The money you invest at the beginning (also called principal).
Contribution: Extra money you add again and again (like every month).
Return rate (percent per year): The average yearly growth you assume before inflation, fees, and taxes.
Compounding: When growth is added to your balance, and future growth happens on the bigger balance.
Inflation-adjusted (today's dollars): A way to show what a future amount might feel like in spending power today, using an inflation rate [2].
Fees: Costs charged by a fund or advisor. In this calculator they reduce your return rate.
Tax on gains (simplified): An optional estimate that taxes only the profit (not what you contributed) [3].
Methodology
What this calculator does
This tool estimates investment growth over time using compound growth with optional recurring contributions. It can also (optionally) adjust for inflation, subtract an annual fee rate, and apply a simplified tax on gains at the end. Results are estimates, not guarantees, because real returns vary over time.
Step 1: Convert annual rates to decimals
Percent inputs are converted to decimals using decimal = percent/100. The estimated return rate is required and must be greater than -100%.
Step 2: Apply fees (optional)
If you enter annual fees, the calculator uses a simple approximation: annual return after fees = annual return - annual fee rate. If this makes the after-fee return less than or equal to -100%, the calculator stops with an error because the math would break or imply a total wipeout each year.
Step 3: Convert the annual return to a periodic rate
The calculator converts the annual after-fee return into a per-compounding-period rate using: periodic rate = (1 + annual return after fees)^(1/periods per year) - 1. Periods per year are mapped as: Annual=1, Semiannual=2, Quarterly=4, Monthly=12, Daily=365. Daily uses a 365-day convention for simplicity.
Step 4: Build the balance over time (iterative schedule)
The calculator simulates the account one period at a time so it can support contribution frequency (monthly or yearly), contribution timing (beginning or end of the period), and a detailed schedule table. Each period follows this order: if contribute at beginning, add the contribution first; compute growth = current balance * periodic rate; add growth to the balance; if contribute at end, add the contribution last.
Step 5: Total contributed and total growth
Total contributed equals starting amount plus all contributions added over the full time horizon. Total growth (future dollars) equals ending balance (after optional fees and taxes) minus total contributed, and it can be negative if the assumed return is negative.
Step 6: Tax on gains at the end (optional simplified model)
If you enter an effective tax rate on gains, the calculator taxes gains one time at the end: taxable gains = max(0, ending balance before tax - total contributed); ending balance after tax = ending balance before tax - taxable gains * tax rate. This matches the idea that capital gains can be taxable, but it is a simplified estimate and not a full tax model [3].
Step 7: Inflation-adjusted ending balance (optional)
If you enter an inflation rate, the calculator shows an inflation-adjusted ending balance (today's dollars): real ending balance = nominal ending balance / (1 + inflation rate)^years. If inflation is blank, the inflation-adjusted output shows N/A instead of assuming 0% inflation [2].
Step 8: Low and high return scenarios (optional)
If you enter a return variance, the calculator also computes a low case using (return rate minus variance) and a high case using (return rate plus variance). If either scenario would make the return less than or equal to -100%, the calculator shows an error so you can adjust the inputs.
Validation and safety rules
Required fields must be valid numbers (no blanks for the return rate). Optional percent fields can be blank, but if you type something non-numeric the calculator shows an error. Tax rate must be from 0 to 100. To prevent overflow and huge tables, the calculator limits total compounding periods to 1,200; if your inputs would exceed that, reduce years or choose a less frequent compounding option. If any intermediate value becomes non-finite (NaN or Infinity), the calculator stops and shows an input error instead of displaying broken results.
Schedule table display
The schedule table reports each period's beginning balance, contribution, growth for the period, and ending balance. If you pick monthly detail and the schedule is very long, the calculator may show the first and last few rows and clearly note that the middle rows were truncated, while still computing the final totals using all periods.