Compound Interest Calculator

At 5% compounded annually, 1000 plus 0 per period grows to about 1628.89 over 10 years.

How it works

• Converted the annual rate to the periodic rate for the chosen compounding frequency.
• Compounded the lump sum over all periods.
• Added the future value of the recurring contributions, if any.
• Subtracted the total contributed to report the interest element.

A = P(1+r/n)^(nt) = 1000 × (1 + 5/100/1)^10

• A constant rate and a constant contribution are assumed; real returns vary and are not guaranteed.
• Taxes, fees and inflation are not modelled. This is an illustration for information only, not investment advice.

Methodology

1. Compound the lump sum with A = P(1 + r/n)^(nt), where r is the annual rate, n the periods per year and t the years.
2. Add the future value of an ordinary annuity for the recurring contributions: PMT·(((1+r/n)^(nt) − 1)/(r/n)).
3. A 0% rate reduces the contribution term to PMT·n·t.
4. Round every monetary value half-up to the selected decimals.

Usage

1. Enter the starting principal and the annual interest rate.
2. Enter the term in years and choose the compounding frequency.
3. Optionally enter a recurring contribution per compounding period and read the future value.

Examples

These are examples, not current values: they use fixed inputs, while the interactive tool computes live results in your browser.

Lump sum, annually

{
  "principal": 1000,
  "annualRatePercent": 5,
  "years": 10,
  "compounding": "annually"
}

Lump sum, monthly

{
  "principal": 1000,
  "annualRatePercent": 5,
  "years": 10,
  "compounding": "monthly"
}

Monthly contributions

{
  "principal": 1000,
  "annualRatePercent": 5,
  "years": 10,
  "compounding": "monthly",
  "contribution": 100
}

Limitations

Stated assumptions

The calculator assumes a single nominal annual rate, compounding at a fixed frequency, and the same contribution each period. It ignores tax, fees, inflation and any change in the rate. Because none of those are known in advance, the output is a scenario rather than a forecast, and it is not investment advice.