Finance

Compound Interest Calculator

A compound interest calculator with monthly, quarterly, daily and annual compounding. Visualise the hockey-stick of compounding with optional regular contributions on top.

Initial principal

Annual rate (%)

Years

Compounding frequency

Monthly contribution (optional)

Leave at 0 for principal-only growth.

Final amount

$110,033

Total contributed

$58,000

Interest earned

$52,033

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

Enter the initial principal — the amount you start with.
Set the expected annual interest rate. Use the rate the bank quotes you (or a conservative average for investments).
Enter the time horizon in years.
Choose how often interest is compounded — most savings accounts compound monthly or daily.
Optionally add a regular monthly contribution to see how it accelerates growth.
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 $110,033 · Interest $52,033

A modest contribution doubles the principal in 20 years.

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

Final $21,724

Pure compound growth — 21× the original principal.

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

Final $82,068

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.

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.