BYTETOOLS

Compound Interest Calculator

Calculate compound interest with optional monthly contributions. See final balance, total interest and a year-by-year growth table for any rate and term.

$34,581.90
Final balance
$12,581.90
Total interest earned
$12,000.00
Total contributions

Year-by-year growth

YearContributedInterestBalance
1$1,200.00$650.33$11,850.33
2$2,400.00$1,414.79$13,814.79
3$3,600.00$2,300.42$15,900.42
4$4,800.00$3,314.67$18,114.67
5$6,000.00$4,465.50$20,465.50
6$7,200.00$5,761.33$22,961.33
7$8,400.00$7,211.09$25,611.09
8$9,600.00$8,824.28$28,424.28
9$10,800.00$10,610.98$31,410.98
10$12,000.00$12,581.90$34,581.90

Estimates only, not financial advice. Contributions are assumed to be spread evenly across each compounding period.

  • Compounding annually, semi-annually, quarterly, monthly or daily
  • Optional recurring monthly contributions
  • Final balance, total interest and total contributions at a glance
  • Year-by-year growth table you can expand or hide
  • Works with any currency symbol — no live rates fetched
  • 100% in-browser and private; estimates only, not advice

How to use the Compound Interest Calculator

  1. 1

    Choose your currency symbol and enter the starting principal.

  2. 2

    Enter the annual interest rate and the number of years.

  3. 3

    Pick a compounding frequency (annually, monthly, daily and more).

  4. 4

    Optionally add a monthly contribution to model regular saving.

  5. 5

    Read the final balance, interest earned and the year-by-year growth table.

About the Compound Interest Calculator

The ByteTools Compound Interest Calculator shows how savings and investments grow when interest earns interest over time. Enter your starting principal, annual rate, term and compounding frequency, add an optional monthly contribution, and instantly see the final balance, total interest and total contributions.

It is built for savers, investors and students comparing accounts or planning long-term goals. A year-by-year table breaks down exactly how contributions and compound growth stack up, so you can see the effect of time and frequency clearly.

Everything is calculated locally in your browser — no numbers are uploaded or stored. Results are estimates for planning only and are not financial advice; your real return depends on the actual account terms.

Frequently asked questions

How is compound interest calculated?

Compound interest is worked out with the 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 time in years. Because each period's interest is added to the balance, the next period earns interest on a larger amount.

What is the difference between compound and simple interest?

Simple interest is calculated only on the original principal, so it grows in a straight line. Compound interest is calculated on the principal plus all previously earned interest, so the balance grows faster over time. The longer the term, the bigger the gap between the two.

How does compounding frequency affect returns?

More frequent compounding earns slightly more because interest is added to the balance sooner and starts earning its own interest. Daily compounding beats monthly, which beats annual, at the same nominal rate — though the difference is usually small compared with the rate and term themselves.

How are monthly contributions handled?

The calculator adds your monthly contribution over the term and grows it at the same rate as the principal, spreading it evenly across each compounding period. This models regular saving, such as paying into an account every month, alongside your initial lump sum.

Are my numbers sent anywhere?

No. All calculations run entirely in your browser with JavaScript. Nothing you type is uploaded, logged or stored, so you can plan your finances privately on any device.

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