What is compound interest?

Compound interest is interest earned on both your original money and on previously earned interest. Over long periods this produces exponential growth — the reason starting early matters so much for saving.

What is the compound interest formula?

A = P(1 + r/n)^(nt), where P is the principal, r the annual rate, n the number of compounding periods per year, and t the number of years. Regular contributions are added at the end of each period in this calculator.

Is this a prediction of investment returns?

No. It's a mathematical projection at a constant rate you choose. Real investment returns vary year to year, and this tool is not financial advice.

Compound Interest Calculator

Calculate the future value of an investment or savings account with compound interest. Set an initial amount, optional monthly contributions, an annual interest rate, and a time horizon, then choose how often interest compounds. The tool shows the final balance, total contributions, and total interest earned, plus a year-by-year breakdown that makes the snowball effect visible.

Calculators

Initial amount ($)

Monthly contribution ($)

Annual rate (%)

Years

Compounding

Final balance: $144,573
Total contributed: $58,000
Interest earned: $86,573

Year-by-year breakdown

Year	Contributed	Interest	Balance
1	$12,400	$801	$13,201
2	$14,800	$1,834	$16,634
3	$17,200	$3,115	$20,315
4	$19,600	$4,662	$24,262
5	$22,000	$6,495	$28,495
6	$24,400	$8,633	$33,033
7	$26,800	$11,100	$37,900
8	$29,200	$13,918	$43,118
9	$31,600	$17,114	$48,714
10	$34,000	$20,714	$54,714
11	$36,400	$24,747	$61,147
12	$38,800	$29,246	$68,046
13	$41,200	$34,244	$75,444
14	$43,600	$39,776	$83,376
15	$46,000	$45,882	$91,882
16	$48,400	$52,603	$101,003
17	$50,800	$59,983	$110,783
18	$53,200	$68,070	$121,270
19	$55,600	$76,915	$132,515
20	$58,000	$86,573	$144,573

A constant-rate projection for education — real returns vary. Not financial advice.

Private by default

This tool runs entirely in your browser. Your data is never uploaded to a server.

How to use

4 clear steps.

Enter your starting amount and optional monthly contribution.
Set the expected annual interest rate and the number of years.
Choose the compounding frequency (monthly, quarterly, or annually).
Review the final balance and the year-by-year growth table.

Good to know

Frequently asked questions

What is compound interest?: Compound interest is interest earned on both your original money and on previously earned interest. Over long periods this produces exponential growth — the reason starting early matters so much for saving.
What is the compound interest formula?: A = P(1 + r/n)^(nt), where P is the principal, r the annual rate, n the number of compounding periods per year, and t the number of years. Regular contributions are added at the end of each period in this calculator.
Is this a prediction of investment returns?: No. It's a mathematical projection at a constant rate you choose. Real investment returns vary year to year, and this tool is not financial advice.