Compound Interest
WEBSee how your savings grow with compound interest and monthly contributions.
Estimates only. Assumes a fixed rate and deposits at the start of each month — real returns vary and this is not financial advice.
What is the Compound Interest tool?
This compound interest calculator projects how a starting deposit grows over time once interest is earned on top of interest. Enter your initial amount, an annual interest rate, how many years you plan to stay invested and how often the interest compounds — yearly, quarterly, monthly or daily — and the future value updates instantly. Add an optional monthly deposit and it is treated as a contribution at the start of every month, so the projection matches how real savings accounts and index funds actually accumulate.
The result panel splits your final balance into two parts: the money you put in (your initial deposit plus every monthly contribution) and the interest earned on top. A simple bar shows that split at a glance, which makes it easy to see the moment compounding starts doing the heavy lifting — the longer the horizon, the larger the interest slice becomes. Compounding frequency matters too: daily compounding edges out yearly at the same rate, and the tool lets you compare them in one tap.
Everything runs entirely in your browser — nothing about your savings is uploaded or stored, and no account is needed. It is free, works on your phone, and updates as you type so you can model different rates, timelines and deposit amounts in seconds. One honest note: these are estimates that assume a fixed rate and steady deposits. Real returns fluctuate, fees and tax reduce them, and this is a planning aid, not financial advice.
How to use the Compound Interest
- Enter your initial deposit — the amount you are starting with.
- Set the annual interest rate you expect to earn.
- Drag the slider to the number of years you will stay invested.
- Pick how often the interest compounds: yearly, quarterly, monthly or daily.
- Add an optional monthly deposit, then read your future value and the split between contributions and interest.
Frequently asked questions
What is compound interest?
Compound interest is interest earned on both your original money and the interest it has already generated. Because each period's interest is added to the balance and then earns interest itself, savings grow faster over time than they would with simple interest.
How is compound interest calculated?
The future value of a lump sum is principal × (1 + r/n)^(n×t), where r is the annual rate, n is the number of compounding periods per year and t is the number of years. Monthly deposits are added using the future-value-of-an-annuity formula, assuming each deposit lands at the start of the month.
Does compounding frequency really change the result?
Yes, but modestly at normal rates. At the same annual rate, more frequent compounding — daily versus yearly — produces a slightly higher balance because interest is credited and starts earning sooner. Switch the frequency in the tool to see the difference for your numbers.
How do monthly deposits affect the total?
Each monthly deposit is invested and compounds for the rest of the term, so regular contributions often end up contributing more to the final balance than a one-off lump sum. The result panel shows exactly how much of your future value came from deposits versus earned interest.
Is my data private?
Yes. The calculation happens entirely in your browser — your amounts are never uploaded, stored or sent to any server. Once the page has loaded, the calculator even works offline.
Is this a guarantee of future returns?
No. The tool assumes a fixed rate and steady deposits to illustrate how compounding works. Real investment returns vary year to year, and fees and taxes reduce them. Treat the projection as a planning estimate, not financial advice.