Investment Calculator
Enter what you start with, what you add each month, the return and the years, and see what it could grow to.
What this tool does
Your end balance depends on the starting amount, the monthly contribution, the annual return and the time. At 7% a year, 10,000 plus 500 a month for 10 years grows to about 106,639, of which 70,000 is what you paid in. Enter your own figures above to see the balance, the growth and the year-by-year table.
Compounds a starting amount and monthly contributions at the annual return you choose.
Splits the end balance into what you put in and what it earned, and shows each year.
How to use it
- Enter the starting amount and the monthly contribution.
- Enter the expected annual return and the number of years.
- Choose whether contributions are made at the start or the end of each month.
- Read the end balance, the growth and the yearly table.
Why use this calculator
Shows what a starting amount plus regular monthly contributions could grow to, with a year-by-year table of what you paid in and what the growth added. Small regular contributions and a long time do most of the work in investing, but the effect is hard to picture. Seeing the contributed amount beside the growth shows how much of the end balance is your own money and how much is compounding.
Why we built it
We built the investment calculator to split the end balance into what you paid in and what it earned, year by year, since that makes the effect of time and contributions clear. The future value calculator handles a lump sum, and the retirement calculator tests a long-term goal.
If your task goes further, try the Rule of 72 Calculator.
Who this tool is for
- Savers planning monthly investing
- Beginners curious about compounding
- Anyone comparing a lump sum with regular deposits
When to use it
- Planning how much to invest each month for a goal.
- Comparing a lump sum with regular contributions.
- Seeing how a higher or lower return changes the outcome.
- Explaining compounding to someone.
How it works
Each month the balance grows by one twelfth of the annual return, and the contribution is added. With contributions at the end of the month, balance = previous × (1 + r/12) + contribution. The start-of-month option adds the contribution first, so it also earns that month's growth.
Example: 10,000 plus 500 a month at 7% for 10 years. The 10,000 alone grows to about 20,097 and the 120 contributions of 500 grow to about 86,542, for a total near 106,639 on 70,000 paid in.
This is a general-purpose calculation using the figures you enter, with constant assumptions. It is not financial, tax or investment advice, and real results will differ.
A worked example
These are the values the calculator opens with, so you can see exactly what it does with them. Change any value on the page and the result updates; the figures below come from the same calculation.
| Input | Value |
|---|---|
| Currency symbol | $ (dollar) |
| Starting amount | 10000 |
| Monthly contribution | 500 |
| Expected annual return | 7 |
| Years to grow | 10 |
| Contributions are made | At the end of each month |
With those inputs, the calculator returns:
- Balance at the end: $106,639.02
- Total you put in: $70,000.00
- Growth (interest earned): $36,639.02
- Growth as a share of the balance: 34.4%
What you give it, and what you get back
| Item | Details |
|---|---|
| Starting amount | What you invest on day one; can be zero. |
| Monthly contribution | The amount added every month. |
| Annual return and years | The assumed constant return, and 1 to 60 years. |
| Output | End balance, total contributed, growth, and a yearly table. |
Issues you may run into
| What you see | Why it happens | What to do |
|---|---|---|
| The result is much higher than I expected | A high assumed return compounds strongly over many years. | Try a more cautious return and see the range. |
| My real account is lower | Fees, taxes and market falls are not modelled. | Subtract fees from the return you enter. |
| I want a lump sum only | Contributions are optional. | Set the monthly amount to zero. |
| I want inflation-adjusted values | The result is in nominal money. | Enter a return after inflation to approximate today's money. |
Assumptions and limitations
- A constant return is an assumption; real markets vary and can fall.
- Fees, taxes and inflation are not modelled unless built into the return.
- Monthly compounding with monthly contributions only.
Frequently asked questions
How do I calculate investment growth?
Compound the balance each month at the annual return divided by 12 and add the contribution. The calculator does this and shows each year.
What return should I assume?
There is no right number. Broad stock markets have averaged higher returns than savings accounts over long periods, but with big swings. Try several values.
Does it include inflation?
No. The result is in nominal money. Enter a return after inflation to see the result in today's money.
What is the difference between contributions at the start and end of the month?
A start-of-month contribution earns one extra month of growth, so the end balance is slightly higher.
Is this financial advice?
No. It is arithmetic on the numbers you enter, not a forecast or a recommendation.
Is my information sent anywhere?
No. The calculation runs in your browser and your figures never leave the page.
Sources and accuracy
Growth of a starting balance with regular contributions uses the compound growth and annuity formulas of standard time value of money mathematics, with interest compounded at the frequency the user selects.
Figures last checked against the source on . Standards and rates can change — if you are relying on this for something that matters, confirm against the source above. Think a figure is wrong or out of date? Send a correction.