Compound Interest Calculator
See how your savings grow with compound interest over time. Add a starting amount, regular monthly deposits, an interest rate and how often interest is compounded, then read the final balance and a year-by-year breakdown.
Amounts have no currency, so you can use any currency. Results are estimates that assume a fixed rate, with no taxes, fees or inflation.
How to use the Compound Interest Calculator
- Enter your starting amount, and a monthly deposit if you plan to add money regularly (leave it at 0 if not).
- Enter the yearly interest rate and the number of years, then choose how often interest is compounded.
- Read the future value, the total you put in and the interest earned. The table below the result shows the balance at the end of every year.
The compound interest formula
For a single starting amount, the final balance is:
A = P × (1 + r / n) ^ (n × t)
- A is the final amount
- P is the initial amount (principal)
- r is the annual interest rate as a decimal (7% = 0.07)
- n is how many times per year interest is compounded
- t is the number of years
With regular deposits, this calculator adds each deposit month by month and lets it earn interest from the time it is added, using the effective monthly rate that matches your compounding frequency.
Examples
Starting amount only: 10,000 at 7% for 10 years grows to about 19,671.51 with yearly compounding, 20,015.97 with quarterly compounding, 20,096.61 with monthly compounding and 20,136.18 with daily compounding. The more often interest is added, the more you earn, but the gain gets smaller each time.
With monthly deposits: 10,000 at 7%, compounded monthly, with 200 added at the end of each month for 10 years grows to about 54,713.58. You deposited 34,000 in total (10,000 plus 120 × 200), so about 20,713.58 of the balance is interest.
Compound interest vs simple interest
Simple interest is only paid on the original amount. At 7% for 10 years, 10,000 earns 7,000 in simple interest, for a total of 17,000. With compound interest, you also earn interest on past interest, which gives 19,671.51 with yearly compounding. You can compare the two with our Simple Interest Calculator.
The rule of 72
A quick way to estimate how long money takes to double is to divide 72 by the annual rate. At 7%, 72 ÷ 7 is about 10.3 years (the exact figure is 10.24 years). It is only an estimate, but it is useful for quick comparisons.
What affects how fast money grows
- Interest rate: a higher rate grows the balance faster, but real returns can change from year to year.
- Time: the longer money stays invested, the more interest earns interest. Starting earlier matters more than most people expect.
- Compounding frequency: more frequent compounding adds a little extra, such as monthly instead of yearly.
- Regular deposits: adding money every month often has a bigger effect than the starting amount.
This calculator is for general information only and is not financial advice. Real savings and investments can have changing rates, fees, taxes and inflation, which are not included here.
Frequently asked questions
What is compound interest?
Compound interest is interest earned on both your original money and the interest that has already been added. Over time this makes a balance grow faster than simple interest.
How do I calculate compound interest?
Use A = P(1 + r/n)^(nt). For example, 5,000 at 5% for 5 years, compounded monthly, gives 5,000 × (1 + 0.05/12)^60 = 6,416.79, so the interest earned is 1,416.79.
Does this calculator include monthly contributions?
Yes. Enter a monthly deposit and choose whether it is made at the start or the end of each month. Leave it at 0 to calculate growth of a single lump sum.
Does it matter how often interest is compounded?
Yes, but not by much. More frequent compounding earns slightly more, for example monthly instead of yearly. The interest rate and the number of years usually matter far more.
Why is my real result different from the calculator?
The calculator assumes a fixed rate for the whole period and ignores taxes, fees and inflation. Real accounts and investments often change rates, so treat the result as an estimate.
Is my data stored or uploaded?
No. The calculator is free and everything runs in your browser. The amounts you enter are never uploaded to a server or stored.