Compound Interest Calculator
See how your savings grow with compounding interest over time.
Formula
A = P × (1 + r/n)^(n×t), where P is the principal, r the annual rate (as a decimal), n the compounding periods per year, and t the years. Interest earned = A − P.
Worked example
$10,000 at 7% annual interest compounded monthly for 10 years: A = 10000 × (1 + 0.07/12)^(120) ≈ $20,096.61 — interest earned ≈ $10,096.61.
How to use the compound interest calculator
The calculator needs four inputs. It takes a few seconds to fill in.
- Initial investment (principal): the amount you start with, such as $1,000.
- Annual interest rate (%): the yearly rate, entered as a percentage. Type 8 for 8%.
- Number of years: how long the money stays invested.
- Compounding frequency: choose yearly, half-yearly, quarterly or monthly.
The calculator then shows two results: the final amount and the total interest earned.
A worked example
Say you put in $1,000 at 8% for 10 years, compounded monthly. The calculator returns:
- Final amount: $2,219.64
- Total interest earned: $1,219.64
Your original $1,000 more than doubled, and over half of the final amount came from interest working on interest. To see how much your balance grew in percentage terms, use our percentage change tool.
The formula and what each part does
The calculator uses this standard formula:
A = P × (1 + r/n)(n×t)
- A is the final amount.
- P is the principal, your starting amount.
- r is the annual rate as a decimal (8% becomes 0.08).
- n is how many times per year interest is added: 1 for yearly, 2 for half-yearly, 4 for quarterly, 12 for monthly.
- t is the number of years.
Total interest is simply A minus P.
Why compounding frequency matters
The more often interest is added, the sooner it starts earning interest of its own. Here is $10,000 at 7% for 10 years:
| Compounding | Final amount | Interest earned |
|---|---|---|
| Yearly | $19,671.51 | $9,671.51 |
| Quarterly | $20,015.97 | $10,015.97 |
| Monthly | $20,096.61 | $10,096.61 |
Monthly compounding earns about $425 more than yearly here. The gap is real but modest. The rate and the time horizon matter far more.
Compound vs. simple interest
Simple interest pays only on the original principal. On the same $10,000 at 7% for 10 years, simple interest adds $7,000, for a total of $17,000. Monthly compounding reaches $20,096.61. That is $3,096.61 more, with no extra effort from you.
The same math works against you on debt, which you can see by running your numbers through a loan EMI calculator.
Time beats rate: why starting early wins
It is tempting to chase a higher rate. But time often does more work than rate. Compare two people who each invest $5,000 once, compounded yearly:
| Scenario | Rate | Years | Final amount | Interest earned |
|---|---|---|---|---|
| Starts early | 7% | 30 | $38,061 | $33,061 |
| Starts later | 10% | 20 | $33,637 | $28,637 |
The 7% investor ends up about $4,400 ahead, even though the other rate is three points higher. The extra ten years gave compounding more time to build on itself, and the growth curve gets steeper the longer it runs.
The takeaway is practical. A smaller amount started sooner can beat a bigger bet started late. Try both setups in the calculator with your own numbers.
A caveat worth knowing: these figures are nominal, meaning before inflation and taxes. Both will reduce what your money can actually buy, so treat the results as an upper-end view of growth.
The Rule of 72: doubling time in your head
The Rule of 72 is a quick mental shortcut. Divide 72 by the annual interest rate to estimate how many years it takes your money to double.
- 8%: 72 ÷ 8 = 9 years. Check: $1,000 at 8% compounded yearly for 9 years grows to about $1,999.
- 6%: 72 ÷ 6 = 12 years. Check: $1,000 at 6% for 12 years grows to about $2,012.
Both checks land very close to $2,000, which is why the rule is so handy.
It is an estimate, not an exact answer. It works best for rates of roughly 6% to 10%, and it drifts at very low or very high rates. For a precise figure, enter your numbers in the calculator. For more on how compounding works, see the U.S. SEC's investor education page on compound interest.
All results here are estimates. Actual returns vary, and past performance does not guarantee future results.
Frequently asked questions
What is compound interest?
Compound interest is interest calculated on both your original amount and the interest already added. Over time, your balance grows faster because earlier interest starts earning its own.
How is compound interest different from simple interest?
Simple interest is calculated only on the original principal, so it grows in a straight line. Compound interest is calculated on a growing balance. On $10,000 at 7% for 10 years, simple interest gives $17,000, while monthly compounding gives $20,096.61.
What does compounding frequency mean?
It is how often interest is added to your balance during the year. This calculator offers yearly, half-yearly, quarterly and monthly. More frequent compounding gives a slightly higher result at the same rate.
How long will it take to double my money?
A quick estimate is the Rule of 72: divide 72 by your annual rate. At 8%, that is about 9 years. For an exact figure, enter your numbers into the calculator and check when the final amount reaches twice your principal.
Does the calculator account for inflation or taxes?
No. It shows nominal growth only, before inflation and taxes. Your real purchasing power will usually be lower, so treat the results as estimates rather than guarantees.
