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Finance

Compound Interest Calculator

Calculate compound interest with optional monthly contributions. See how your savings grow with daily, monthly, quarterly, or annual compounding.

Leave at 0 for principal-only growth.

Final amount

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Total contributed

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Interest earned

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Growth over time

Method

How this calculator works

Compound interest is the future value of a principal, optionally augmented by recurring contributions, after compounding repeatedly over time.

A = P × (1 + r/n)^(n×t)
+ contribution × ((1 + r/n)^(n×t) − 1) / (r/n)

P = principal
r = annual rate (decimal)
n = compounding periods per year
t = time in years
A = final amount
  1. Enter the initial principal — the amount you start with.
  2. Set the expected annual interest rate. Use the rate the bank quotes you (or a conservative average for investments).
  3. Enter the time horizon in years.
  4. Choose how often interest is compounded — most savings accounts compound monthly or daily.
  5. Optionally add a regular monthly contribution to see how it accelerates growth.
  6. The calculator combines the lump-sum future value with the annuity future value of contributions.

Examples

Worked examples

Real numbers, end-to-end results.

$10,000 · 7% · 20 years · monthly · +$200/mo

Final $144,573 · Interest $86,573

A modest monthly contribution turns $58K invested into $144K over 20 years.

$1,000 · 8% · 40 years · annually · no contributions

Final $21,725

Pure compound growth — 21× the original principal.

$50,000 · 5% · 10 years · quarterly · no contributions

Final $82,181

A conservative 5% rate still produces 64% growth in a decade.

Use cases

When to use it

  • Estimate the future value of a savings account or fixed deposit.
  • See how starting an additional contribution today changes the 30-year picture.
  • Compare different compounding frequencies before choosing a savings product.
  • Demonstrate the time-value of money to children, students, or anyone learning to save.

Enter values in your preferred currency. Results are returned in the same currency.

Disclaimer: This calculator provides estimates for informational and educational purposes only. It is not a substitute for professional financial advice, tax planning, or investment guidance. Always consult a qualified financial advisor or accountant for decisions affecting your finances.

Sources: Uses compound interest formula A=P(1+r/n)^(nt). Compounding frequency as specified by the user.

FAQ

Frequently asked questions

What is compound interest?
Compound interest is interest paid on both the principal and the interest already earned. It causes savings (or debt) to grow exponentially over long horizons.
How is this different from simple interest?
Simple interest pays only on the principal — it grows linearly. Compound interest pays on principal + previously-earned interest, so growth accelerates the longer the money stays invested.
Does compounding frequency really matter?
It matters a little. Daily compounding beats annual compounding for the same nominal rate, but the difference is usually under 0.1% per year. The variable that dominates is the rate itself, not the frequency.
How does the contribution box work?
A contribution is added at the end of every compounding period and immediately starts earning interest. This calculator combines the lump-sum future value with an annuity future value for the contributions.
Why does the chart bend upward?
Because the interest earned each year is calculated on a larger and larger balance. Early years grow slowly; later years grow dramatically. This is the famous "hockey stick" of compounding.
Methodology, assumptions & limitations

How we calculate: This calculator uses standard, peer-reviewed mathematical formulas implemented in TypeScript. All calculations run entirely in your browser — no data is sent to any server.

Assumptions: Unless stated otherwise, calculations assume constant rates over the specified period, no taxes or fees beyond those explicitly input, and standard compounding conventions for the formula type.

Limitations: Results are estimates for planning purposes. Real-world outcomes may differ due to variable rates, regulatory changes, taxes, fees, inflation, or other factors not modeled. This tool does not constitute financial, tax, or investment advice.

When NOT to use this: Do not rely solely on this calculator for major financial decisions such as mortgages, retirement planning, or tax filing without consulting a qualified financial advisor or accountant.

Feedback: Found an error or have a suggestion? Contact us — we review and correct reported issues within 48 hours.

Deep Dive Guide

Compound Interest Explained — Why Einstein Called It the Eighth Wonder

A complete guide to compound interest: the formula, how compounding frequency matters, the Rule of 72, real-world examples, and why time is your most powerful asset.

Read Full Guide

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