Investment Calculator

Before you enter your numbers

Enter the balance invested now and the amount added at each month end. Use an annual return compatible with your holdings and costs. If your expected return is already net of fees, do not subtract them again. There is no separate tax or inflation field on this page.

• Starting investment
• Monthly contribution
• Investment period
• Expected annual return

Input reference

• Starting investment: The current balance committed to this goal. Use a recent statement and exclude money reserved for unrelated goals. This starting value is already invested, so do not also enter it as a recurring contribution.
• Monthly contribution: New money added at the end of each month. Convert annual saving to a monthly amount by dividing by 12. This page does not schedule skipped months or one-time deposits automatically.
• Years: The duration of the calculation in years. Longer periods give growth or withdrawals more time to operate. This is a chosen modeling horizon, not a prediction of an investment term or your lifetime.
• Annual return: An assumed nominal annual rate, divided by 12 in monthly projections. It is held constant. It is not a guaranteed yield, and the default should be replaced with an assumption suited to your scenario.

Formula and calculation method

Future value = P × (1 + i)^n + C × [(1 + i)^n − 1] / i, where P is the starting balance, C is the monthly contribution, i is annual return / 12 and n is the number of months. At zero return, future value is P + C × n.

Worked example

With 10,000 invested, 200 added monthly and ten years at a 6% nominal annual rate compounded monthly, the projected balance is about 50,970. Contributions total 34,000, leaving about 16,970 of modeled growth. This is an illustration, not a return forecast.

How to interpret the result

The result panel reports future value, total contributions and estimated investment growth.

A smooth curve can hide severe temporary losses. Money needed for a near-term expense may require a different risk approach from money invested for decades. Run lower-return scenarios and compare a higher contribution separately so that saving effort is not confused with investment performance.

Where investment growth comes from

The final balance has three components: the amount you started with, the contributions you added, and investment growth. The calculator compounds returns monthly and treats contributions as regular monthly deposits.

Use a lower return assumption when you want a stress test. A small change in annual return can have a large effect over 20 or 30 years because each year’s growth becomes part of the base that can grow in later years.

Understand the return convention

A 6% nominal annual input compounded monthly produces an effective annual growth rate slightly above 6%. If your source quotes a geometric annual return, the difference in convention can matter over a long horizon. The model is deliberately simple and documents its monthly rate rather than claiming to duplicate every investment reporting standard.

For a contribution increase, compare a second run using the higher monthly amount. The difference includes both additional deposits and the growth those deposits earn. Do not call the entire difference extra investment profit; the contribution and growth breakdown explains where it comes from.

Use a return range instead of treating one forecast as a promise

An investment projection is highly sensitive to return and time. Run at least a lower, central and higher return scenario, and keep fees and taxes separate unless they are explicitly included. The purpose is to see the range created by assumptions, not to identify the return the market will deliver.

For irregular deposits or withdrawals, a simple fixed monthly contribution model is only an approximation. Update the starting balance and contribution amount periodically so the projection reflects what has actually happened.

Use The Result In The Next Calculation

If you want to understand performance rather than future growth, move to the investment return calculator. If the investment is part of a retirement plan, transfer the projected future value into the retirement calculator using the same date and nominal or real basis.