Everything runs locally in your browser. Your figures are never uploaded or stored, the projection updates on every keystroke, and the breakdown separates your own money (principal plus contributions) from the interest the compounding adds - so you can see exactly how much of the final balance is growth. It works offline once the page has loaded, and the numbers are currency-agnostic, so read them as dollars, euros, rupees or anything else.
Free Compound Interest Calculator
Runs entirely in your browser - no upload, no sign-up.
Your investment
Final balance
19,318.14
- Starting principal
- 1,000.00
- Total contributions
- 12,000.00
- Total interest earned
- 6,318.14
- Total deposited
- 13,000.00
Results update as you type. Contributions are added at the end of each compounding period. Decimals (dot or comma) work - nothing is uploaded.
How do you calculate compound interest?
Compound interest is calculated with A = P(1 + r/n)^(nt): the principal P grows by the annual rate r, compounded n times a year over t years. This free compound interest calculator adds your regular contributions on top and shows the final balance, the total interest earned and everything you paid in - live as you type.
How to use
- 1Enter your starting deposit and rate. Type the initial principal and the annual interest rate as a percent (for example 5 for 5%).
- 2Pick a compounding frequency and duration. Choose daily, monthly, quarterly or annually, and set how many years the money grows - fractional years like 7.5 are fine.
- 3Add optional contributions and read the result. Enter a regular contribution per period if you save more each cycle. The final balance, total interest and total contributions update instantly; use Copy to grab the balance.
Who it's for
- Long-term savers projecting how a nest egg grows at a fixed rate with a steady monthly top-up.
- Investors comparing daily, monthly, quarterly and annual compounding to see how much the frequency actually changes the outcome.
- Students checking compound-interest homework against the worked A = P(1 + r/n)^(nt) formula.
- Anyone weighing a savings account or CD who wants the real final balance, not just the headline rate.
- Goal planners testing how a bigger deposit or a longer horizon changes the interest earned.
FAQ
Is this compound interest calculator free?
Yes - 100% free, no sign-up and no limits. The whole projection runs in your browser with plain JavaScript, so it also works offline once the page has loaded.
Are my numbers uploaded anywhere?
No. The math happens locally on your device. Nothing you type - deposit, rate, or contributions - is sent to a server, stored, or shared. Close the tab and it is gone.
What is the compound interest formula?
For a lump sum it is A = P(1 + r/n)^(nt), where P is the principal, r the annual rate as a decimal, n the number of compounding periods per year, and t the time in years. Regular deposits add a second term, PMT × [(1 + r/n)^(nt) - 1] ÷ (r/n).
How are regular contributions handled?
Each contribution is added at the end of every compounding period and then earns interest for the rest of the term. The contribution matches the compounding frequency you pick: choose monthly and it is deposited 12 times a year, quarterly and it is deposited 4 times a year, annually and it is deposited once a year. Set it to 0 to project a lump sum with no top-ups.
Does the compounding frequency really change the result?
A little. More frequent compounding pays interest on interest sooner, so daily beats annually - but the gap is small. At 5% over 30 years the difference between annual and daily compounding is only around 3.7%, while raising the rate or extending the term changes the balance far more.
What is the difference between compound and simple interest?
Simple interest is paid only on the original principal, so it grows in a straight line. Compound interest is paid on the principal plus all interest already earned, so the balance curves upward and accelerates - the longer the horizon, the wider the gap between the two.
What interest rate should I use?
Use the annual percentage yield (APY) if you have it, since that already reflects compounding, or the nominal annual rate the account quotes. Enter it as a percent - the calculator converts it to a decimal and divides by your chosen number of periods internally.