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Compound Interest Calculator
Estimate how a starting amount could grow with compound interest and optional recurring contributions.
Use this calculator to estimate compound growth from an initial amount, annual interest rate, time period and optional recurring contributions.
This is a planning estimate only. Actual savings or investment returns can vary and may not compound at a constant rate.
Enter a nonnegative annual percentage rate and a positive time period. Contributions are optional and occur at period end. Without contributions, the formula uses the exact entered time. With contributions, years convert to months and round to the nearest whole month; months must be whole numbers. Weekly and daily compounding use equivalent monthly growth factors; other frequencies apply growth on their monthly boundaries. Rates remain constant. Dollar amounts use a generic dollar sign, without currency conversion.
Calculations run locally in your browser. Your financial inputs are not saved.
Set your growth assumptions and optional contributions.
Example: Long-Term Savings Growth
Static example: $10,000 at an annual rate of 5% compounded monthly for 10 years, without recurring contributions, uses FV = $10,000 × (1 + 0.05 / 12)^(12 × 10). The estimated future value is $16,470.09, including $6,470.09 of interest. Values are displayed to cents.
About this calculator
Understanding Compound Growth
Compound interest means growth is calculated on both the original principal and previously accumulated interest.
- Recurring contributions can have a substantial impact on future value, particularly over longer time periods.
- Contributions occur at the end of their monthly, quarterly or annual periods. Earlier contributions have longer to compound.
- More frequent compounding generally increases effective growth at the same positive nominal annual rate. Weekly uses 52 periods per year; daily uses 365.
- This calculator assumes a constant annual rate for planning purposes. Actual savings or investment returns may vary.
Compound Interest Formula
For principal only, A = P × (1 + r/n)^(n × t). A is future value, P is starting principal, r is the annual rate as a decimal, n is compounding periods per year, and t is years. Interest earned is A minus P.
Regular Contributions and Simple Interest
With contributions, total invested is the starting principal plus all recurring additions. Interest earned is future value minus total invested. Compound interest earns interest on accumulated interest; simple interest uses only the original principal. Use the related Simple Interest Calculator for that calculation. Taxes, fees, inflation and changing returns are not included.
Example: Contributions with No Interest
Static example: starting from $0, contributing $100 per month at 0% for 1 year produces $1,200 of contributions, $0 interest and a $1,200 ending balance.
Frequently asked questions
What is compound interest?
Compound interest calculates interest on the original principal and previously accumulated interest. The principal-only formula is A = P × (1 + r/n)^(n × t).
How often can interest be compounded?
This calculator supports annual, semiannual, quarterly, monthly, weekly and daily compounding, using 1, 2, 4, 12, 52 and 365 periods per year respectively. Actual account terms may differ.
Is monthly compounding better than annual compounding?
At the same positive nominal annual rate, monthly compounding produces a higher modeled future value because accumulated interest starts earning interest sooner. This mathematical comparison is not an account or investment recommendation.
What is the difference between simple and compound interest?
Simple interest is calculated only on the original principal. Compound interest also earns interest on accumulated interest. The related Simple Interest Calculator handles the simple-interest formula separately.
How do regular contributions affect compound growth?
Regular additions increase total invested and can earn interest over subsequent periods. This calculator adds contributions at the end of their selected monthly, quarterly or annual periods and keeps them separate from interest earned.
Does this calculator account for taxes, fees or inflation?
No. These are general estimates using a constant entered rate. Taxes, investment fees, inflation and changing interest rates are not automatically modeled. Results are not financial, investment, tax, lending or legal advice.
This calculator provides general planning estimates only and is not financial, investment, tax or legal advice. Actual returns, rates and account terms may differ.