Compound Interest Calculator
Project the future value of an initial deposit with optional monthly contributions. Choose annual, semiannual, quarterly, monthly, or daily compounding to explore how a nominal annual rate affects growth.
Compound Interest Calculator tool
About the Compound Interest Calculator
The results separate total contributions, including your starting principal, from interest earned. A yearly table helps long-term savers compare consistent contribution plans. Results are estimates, not financial advice.
How Is Compound Interest Calculated?
Without contributions, the standard compound-growth expression applies directly. For monthly deposits, the selected compounding convention is converted into an equivalent monthly rate; deposits are added at month end. This is a mathematical projection rather than a bank-specific posting schedule.
Without deposits: FV = P × (1 + R/k)^(k × t)
Monthly equivalent rate: i = (1 + R/k)^(k/12) − 1
With deposits: FV = P × (1 + i)^N + C × [(1 + i)^N − 1] ÷ i
At 0%: FV = P + C × N
Example
$1,000 at a nominal 12% compounded monthly for one year with $100 deposited at each month end grows to $2,395.08. Contributions total $2,200 and interest is $195.08.
How to Use the Compound Interest Calculator
- Enter the starting principal.
- Enter the nominal annual rate.
- Choose the compounding frequency.
- Enter a duration that represents a whole number of months.
- Enter the monthly contribution, or zero for a lump sum only.
- Compare future value, contributions, interest, and yearly balances.
Compound Interest Calculator Examples
Annual compounding
A $1,000 lump sum at 5% compounded annually for two years becomes $1,102.50.
Zero-rate deposits
Starting with $1,000 and adding $100 monthly for two years at 0% produces $3,400.
Contribution totals
Total contributions include the starting principal plus all monthly deposits. Interest earned is future value minus that total.
Compounding frequency
More frequent compounding increases the effective yield for the same positive nominal rate. Daily compounding uses 365 periods per year; it does not model calendar dates.
Frequently Asked Questions
When are contributions made?
At the end of each month, after that month’s growth.
Is the entered rate APY?
No. It is a nominal annual rate. Compounding determines the effective annual yield.
How are annual compounding and monthly deposits combined?
The model uses an equivalent monthly growth rate so each deposit earns growth from its deposit date.
Can I enter a partial year?
Yes, if it corresponds to whole months, such as 0.5 years for six months.
Does the forecast include investment risk or inflation?
No. It assumes a constant nonnegative return and excludes volatility, inflation, taxes, and fees.