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- Enter an initial amount, interest rate and time to see the future value.
- Choose yearly, half-yearly, quarterly, monthly, daily or continuous compounding.
- Add a monthly contribution at the start or end of each month.
- Shows interest earned, effective annual rate and years to double.
How to use the compound interest calculator
Choose a currency
Pick $ USD, £ GBP or ₹ INR.
Enter amount, rate and time
Type the starting balance, the yearly interest rate and the number of years. Decimals such as 2.5 years work.
Pick the compounding frequency
Savings accounts often compound daily or monthly, bonds yearly or half-yearly.
Add monthly contributions
Open the advanced options to add a regular deposit and choose whether it is made at the start or end of the month.
The compound interest formula
Future value of a single amount
A = P × (1 + r/n)n × t
P = starting amount, r = yearly rate as a decimal
n = compounding periods per year, t = years
Continuous compounding: A = P × er × t
Interest earned = A − P.
Adding monthly contributions
FV = C × [(1 + g)m − 1] ÷ g
C = monthly contribution, m = number of months
g = equivalent monthly rate = (1 + r/n)n/12 − 1
For contributions at the start of the month, multiply by (1 + g).
Compound interest examples
Example 1: $10,000 at 5% for 10 years
Compounded monthly, no extra deposits.
With simple interest the same deposit would reach only $15,000.
Example 2: add $200 a month
Same $10,000 at 5% monthly, plus $200 at the end of each month.
Regular contributions more than double the interest earned compared with Example 1.
Reference: $10,000 at 5% for 10 years
Future value by compounding frequency.
More frequent compounding helps, but the gain shrinks quickly: daily beats monthly by only about $17 here.
Simple vs compound interest
Simple interest is paid only on the original amount. Compound interest is also paid on interest already earned, so the balance grows faster every year. Over short periods the difference is small, but over decades it becomes the main source of growth. The rule of 72 gives a quick estimate of doubling time: divide 72 by the rate, so money at 5% doubles in roughly 14.4 years.
Where a compound interest calculator helps
Savings accounts
Project the balance of a high-yield savings or ISA account.
Comparing rates
See how APR, APY and compounding frequency affect the result.
Long-term goals
Check how monthly saving builds up over 10, 20 or 30 years.
Debt growth
Understand how unpaid interest grows a balance; see the credit card payoff calculator.
The calculator assumes a constant rate and no fees or taxes. Real savings and investment returns change over time. For Indian deposits use the FD calculator or RD calculator, and for mutual funds the SIP calculator.
Compound interest calculator FAQ
What is compound interest?
It is interest calculated on the starting amount and on interest already added, so your balance grows faster over time than with simple interest.
How often should interest compound?
More often is better for savers, but the difference between monthly and daily compounding is small. The rate matters far more than the frequency.
What is the difference between APR and APY?
APR is the yearly rate before compounding. APY includes compounding. A 5% APR compounded monthly is an APY of about 5.12%.
How long does it take to double my money?
Divide 72 by the interest rate for a quick estimate. The calculator shows the exact figure for your compounding frequency.
Can I use decimal years?
Yes. Enter 2.5 for two and a half years. Monthly contributions are counted for whole months only.
Does the calculator include tax?
No. Interest is shown before tax. Tax rules depend on the country and account type.