Calculator Tools
Estimate a final balance from principal, nominal annual rate, duration and compounding frequency. Add optional end-of-period monthly or annual contributions, review interest separately, and inspect a period summary.
Simple workflow
How to use Compound Interest Calculator
- 1Enter principal, annual rate, duration and compounding frequency.
- 2Optionally add a monthly or annual end-of-period contribution.
- 3Select Calculate estimate to see contributions, interest, final balance and the period summary.
Good to know
Frequently asked questions
Which compound-interest formula is used?
Principal alone uses A = P(1 + r/n)^(nt). Each optional contribution is added at the end of its selected period and compounds for the remaining duration.
Does the estimate include tax, fees or inflation?
No. It is a mathematical estimate using the entered constant nominal rate. It excludes taxes, fees, inflation, rate changes and market risk.
Are negative interest rates supported?
No. This version accepts rates from 0% through 100%. It reports unsupported or overflow-producing values instead of displaying Infinity or NaN.
Is this investment advice?
No. The calculator is an educational arithmetic tool and does not predict returns or recommend financial products.
Practical guide
Estimate mathematical compound growth and end-of-period contributions
For principal alone, compound interest follows A = P(1 + r/n)^(nt): principal P grows at nominal annual rate r, compounded n times per year for t years. More frequent compounding changes how often earned interest becomes part of the balance.
Optional monthly or annual contributions are added at the end of each selected contribution period. Each contribution then compounds for the remaining duration. The summary separates deposited principal and contributions from calculated interest.
Worked example
Compound 1,000 annually at 5%
- Start with
- Initial principal 1,000, annual rate 5%, duration 10 years and no recurring contribution.
- Choose
- Choose annual compounding and calculate.
- You get
- The mathematical final balance is 1,628.89 and calculated interest is 628.89.
Tips for a useful result
- Use the nominal annual rate expected by the compounding agreement you are modelling.
- Choose months when the duration is shorter than a whole year.
- Treat the output as an estimate; it excludes fees, taxes, inflation and changing returns.
Assumptions, limits and privacy
Rates must be from 0% through 100%, duration is capped at 100 years, and amounts are bounded to prevent overflow. Summary amounts are rounded to two decimal places for display while calculations retain greater precision.
This calculator provides mathematical estimates for educational purposes. It does not predict investment returns or provide financial advice. Inputs and results remain in the browser and are not stored or sent to analytics.
Authoritative external sources
- Investor.gov Compound Interest Calculator (external)
An educational U.S. Securities and Exchange Commission resource explaining principal, contributions, time, rate and compounding frequency.
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