Investment calculator
See how savings could grow with compound interest, using a return rate you assume, with optional monthly contributions.
Free to use, no account needed. What you type stays in your browser.
Final balance
$54,713.58
Total you put in
$34,000.00
Interest earned
$20,713.58
This is an illustration at a fixed rate you chose, not a forecast. Real investments rise and fall, can lose money and carry fees and tax that are not included. It is not financial advice.
- Final balance$54,713.58
- Total you put in$34,000.00
- Interest earned$20,713.58
Year by year
| Year | Put in | Interest | Balance |
|---|---|---|---|
| 1 | $12,400.00 | $801.42 | $13,201.42 |
| 2 | $14,800.00 | $1,834.27 | $16,634.27 |
| 3 | $17,200.00 | $3,115.28 | $20,315.28 |
| 4 | $19,600.00 | $4,662.39 | $24,262.39 |
| 5 | $22,000.00 | $6,494.83 | $28,494.83 |
| 6 | $24,400.00 | $8,633.24 | $33,033.24 |
| 7 | $26,800.00 | $11,099.74 | $37,899.74 |
| 8 | $29,200.00 | $13,918.03 | $43,118.03 |
| 9 | $31,600.00 | $17,113.55 | $48,713.55 |
| 10 | $34,000.00 | $20,713.58 | $54,713.58 |
How this is calculated
Savings grow because interest is earned on earlier interest. These are the formulas used:
- Monthly rate
- i = r ÷ 12 ÷ 100
- Final balance
- P × (1 + i)ⁿ + C × ((1 + i)ⁿ − 1) ÷ i
- Total put in
- P + C × n
- Value in today's money
- B ÷ (1 + inflation ÷ 100)^years
P is the starting amount, C is the monthly contribution, r is the assumed annual return in percent, n is the number of months, i is the monthly rate and B is the final balance. Interest is added once a month and each contribution is paid at the end of the month.
The return is a fixed rate you assume. Real investments do not grow in a straight line: they rise and fall, can lose money, and fees and tax reduce what you keep. Past returns do not predict future ones. Use this to compare scenarios, not to forecast.
Growth is calculated without rounding and only the figures shown are rounded to 2 decimal places, so the amount put in plus the interest equals the balance.
Worked example
Starting with $10,000.00 and adding $200.00 a month for 10 years at an assumed return of 7% a year grows to $54,713.58. You put in $34,000.00 and the other $20,713.58 is interest. With 2% inflation a year, that is worth about $44,884.19 in today's money. The return is an assumption, not a promise.
Investment questions
How does compound interest work?
Interest is added to the balance, and from then on the interest earns interest too. 10,000 at 7% a year, compounded monthly, becomes 20,096.61 after 10 years.
What return should I enter?
There is no right answer: it depends on what you invest in, and nobody knows future returns. Try a few rates, such as a low, a middle and a high one, and look at the spread. Do not treat any of them as a forecast.
Why does inflation matter?
Prices rise over time, so the same amount buys less in the future. The figure in today's money divides the final balance by the inflation over the years, to show what it could buy at today's prices.
Are fees and tax included?
No. Fees and tax lower what you keep. To allow for them roughly, enter a lower return, for example the return minus the yearly fee.
Is my information stored or sent anywhere?
No. The calculation runs in your browser. The numbers you enter are not sent to us or saved.
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Results are estimates for planning. They are not financial, tax or religious advice.