Investment Calculator

What is the Investment Calculator?

This calculator estimates what your investment could be worth after a set number of years. You enter what you're starting with, how much you plan to add each month, the return you expect, and how long you'll stay invested. It then shows your final balance, how much of it is your own money, and how much came from growth.

It's useful if you're thinking about an index fund, a brokerage account, a retirement account, or a savings plan, and you want a rough picture before you commit. You can test a one-time lump sum, regular monthly contributions, or both.

Quick answer: If you invest $10,000 today and add $200 a month at an 8% annual return for 20 years, compounding monthly, you'd end up with about $167,072. You'd have put in $58,000 yourself; the other roughly $109,000 would be growth.

How to Use the Calculator

1. Initial investment: the amount you're investing today. Enter 0 if you're starting from scratch.
2. Monthly contribution: how much you'll add every month. Enter 0 for a one-time investment.
3. Annual return rate (%): the yearly return you expect. See the tips below for choosing a sensible number.
4. Investment period (years): how long you plan to keep the money invested.
5. Compound frequency: how often returns are added to your balance. Monthly is the most common choice.
6. Press Calculate.

Your results show the final balance, total contributions, total growth, and ROI. The year-by-year table underneath lets you see how the balance builds over time.

A practical tip: run the same numbers at 6%, 8% and 10%. You'll see a range of outcomes instead of a single number, which is a more honest way to plan.

How the Calculation Works

The calculator uses compound growth: your returns earn returns of their own. The formula for a starting amount plus regular contributions is:

FV = PV × (1 + r)ⁿ + PMT × [((1 + r)ⁿ − 1) / r]

• FV = Future value (your final balance)
• PV = Initial investment
• PMT = Amount added each period (monthly contribution)
• r = Return rate per period (annual rate ÷ number of periods per year)
• n = Total number of periods (years × periods per year)

ROI on this page is total growth divided by total contributions. In the example above: $109,072 ÷ $58,000 = 188%.

A Worked Example

Let's walk through the numbers with a simple case.

• Initial investment: $10,000
• Monthly contribution: $200
• Annual return: 8%
• Period: 20 years
• Compounding: monthly

Step 1: Monthly rate = 8% ÷ 12 = 0.6667% Step 2: Number of periods = 20 × 12 = 240 Step 3: Your $10,000 grows to about $49,268 on its own. Step 4: Your $200 monthly contributions grow to about $117,804. Step 5: Add them together: about $167,072.

• Total you contributed: $58,000
• Total growth: $109,072
• Final balance: $167,072

Notice that growth is almost twice what you put in. Most of that growth arrives in the later years, because the balance is larger by then. That's why starting early matters.

How Return Rate Changes the Outcome

Same inputs as above ($10,000 start, $200 a month, 20 years), only the return rate changes:

• At 6% a year: about $125,510
• At 8% a year: about $167,072
• At 10% a year: about $225,155

A couple of percentage points makes a big difference over two decades. It's also why the return you assume deserves some thought, since no one can know the real figure in advance.

What the Calculator Doesn't Include

To keep things clear, here's what the result leaves out:

• A constant return. Real markets go up and down. Actual results will rarely follow a smooth line.
• Fees. Fund fees and account charges reduce your return.
• Taxes. Tax rules depend on your country and account type.
• Inflation. The result is in today's dollar amounts but future dollars buy less. For example, $167,072 in 20 years with 3% yearly inflation would feel closer to about $92,500 in today's buying power.

Treat the result as an estimate for planning, not a prediction.

Frequently Asked Questions