Find out how much your money can earn.
Simulate compound interest with monthly contributions and see how much you will have in the future.
Compound interest calculator
In 10 years you will have
$118,319.73
- Invested
- $61,000.00
- Interest
- $57,319.73
In 10 years you will have $118,319.73
$61,000.00 invested$57,319.73 in interest
Hover or tap the bars to see each moment.
| Year | Invested | Interest | Total |
|---|---|---|---|
| 1 | $7,000.00 | $468.08 | $7,468.08 |
| 2 | $13,000.00 | $1,756.47 | $14,756.47 |
| 3 | $19,000.00 | $3,969.21 | $22,969.21 |
| 4 | $25,000.00 | $7,223.53 | $32,223.53 |
| 5 | $31,000.00 | $11,651.53 | $42,651.53 |
| 6 | $37,000.00 | $17,402.06 | $54,402.06 |
| 7 | $43,000.00 | $24,642.86 | $67,642.86 |
| 8 | $49,000.00 | $33,562.92 | $82,562.92 |
| 9 | $55,000.00 | $44,375.22 | $99,375.22 |
| 10 | $61,000.00 | $57,319.73 | $118,319.73 |
How to calculate compound interest
Compound interest is interest earned on the initial capital and also on the interest already accumulated, the famous “interest on interest”. That is why the balance grows exponentially: the longer the money stays invested, the bigger the effect. The calculator above simulates it with an initial deposit, monthly contributions, interest rate (per month or per year) and term.
Compound interest formula
Without contributions, the final amount is calculated as:
M = C × (1 + i)^n
Where M is the final amount, C the initial capital, i the rate per period (as a fraction, 1% = 0.01) and n the number of periods. With a monthly contribution P made at the end of each month, add the future value of the installments:
M = C × (1 + i)^n + P × [((1 + i)^n − 1) ÷ i]
Example: $1,000 with $500 monthly contributions
Starting with $1,000.00 and contributing $500.00 per month at 1% per month for 10 years (120 months), you invest $61,000.00 and end up with $118,319.73, of which $57,319.73 is interest.
See the calculation in action
Every month the balance earns interest and only then receives the contribution. This is the first month of the example:
Opening balance
$1,000.00
1% interest
+ $10.00
Contribution
+ $500.00
New balance
= $1,510.00
The second month starts with $1,510.00, and interest now earns interest too. That is why the green part grows faster and faster:
- 1 year$7,468.08
- 5 years$42,651.53
- 10 years$118,319.73
InvestedInterest
Simple interest vs. compound interest
With simple interest the rate always applies to the initial capital; with compound interest, to the accumulated balance. With $10,000.00 at 1% per month for 5 years, simple interest yields $16,000.00, while compound interest yields $18,166.97. The gap widens every month.
Annual or monthly rate: how to convert
In compound interest, the annual rate is not divided by 12. The equivalent monthly rate is (1 + annual rate)^(1/12) − 1. An annual rate of 12% equals 0.9489% per month, not 1%. The calculator does this conversion for you when you choose “per year”.
Rule of 72: how long to double your money
A shortcut to estimate how long a value takes to double is to divide 72 by the rate per period in %. At 1% per month, money doubles in about 72 months (6 years); at 12% per year, in about 6 years. It is an approximation, not an exact calculation.
Frequently asked questions.
What is compound interest?
It is interest calculated on the invested amount plus the interest already accumulated. Each month the earnings join the balance and start earning too, which is why growth speeds up over time.
How is the calculation done?
Month by month: the balance receives the monthly rate and, at the end of the month, the monthly contribution is added. If you enter an annual rate, it is converted to the equivalent monthly rate, not divided by 12.
Does the result consider income tax and inflation?
No. Values are gross and nominal. Taxes, brokerage fees and inflation reduce the real gain, so use the simulation as a reference, not as a promise of return.
Is my data saved?
No. Everything is calculated in your browser, with no sign-up and without sending any value to a server.
How do you calculate compound interest?
Multiply the capital by (1 + rate) raised to the number of periods: M = C × (1 + i)^n. With monthly contributions, the future value of the installments is added as well. The calculator does this month by month and shows the growth chart.
What is the difference between simple and compound interest?
With simple interest the rate always applies to the initial amount. With compound interest it applies to the accumulated balance, including previous interest, so growth is larger over the long run.
How do you convert an annual rate into a monthly rate?
Use (1 + annual rate)^(1/12) − 1. In compound interest you do not divide the annual rate by 12: 12% per year equals about 0.95% per month.
How much does $1,000 a month earn with compound interest?
It depends on the rate and the term. Enter the amount in the monthly contribution field, the expected rate and the period in the calculator to see the total accumulated, how much was invested and how much came from interest.