Investment Calculator

How this investment calculator works

This tool projects the future value of an investment when you start with a balance and add a fixed contribution every month, earning a constant annual return that compounds monthly. It is a planning sketch for retirement accounts, brokerage savings, or any goal where regular deposits matter as much as the starting amount.

What the model assumes

Returns are constant every month. Real markets go up and down; sequence of returns, fees, and taxes can change outcomes a lot. Treat the result as “if I earned this average return steadily,” not as a promise.

Formula idea

The starting balance compounds for the full period. Each monthly contribution compounds for the remaining months after it is added. The combined future value is the sum of those pieces. The page also shows how much of the ending balance came from contributions versus growth.

Worked example

Start with $5,000, contribute $300 per month for 20 years, and assume 7% annual return compounded monthly. The ending balance is typically tens of thousands higher than contributions alone, because early deposits have many years to grow. Raising the monthly contribution usually moves the needle more than a small rate tweak over the same horizon.

How to use it

1. Enter your current invested balance (use 0 if you are starting from scratch).
2. Enter the monthly amount you can invest.
3. Enter an assumed annual return as a percent (historical averages are not guarantees).
4. Enter the number of years you plan to keep contributing.
5. Review projected balance and total contributions, then stress-test with a lower return.

Frequently asked questions

What return rate should I assume?

There is no guaranteed rate. Try a conservative and an optimistic assumption and plan against the lower outcome. Past market averages are not promises.

Are contributions assumed at the beginning or end of each month?

This model treats contributions as a regular monthly deposit in a standard future-value of annuity style calculation. Exact payroll timing can differ slightly.

Limitations

No inflation adjustment, expense ratios, or tax drag. Results are estimates only and are not financial advice.

Results are estimates only and are not financial advice.