The rate you type is most of the answer
The compound interest calculator projects a balance forward from a starting amount and a regular contribution, and works backwards from a target to the monthly deposit that reaches it. Both directions come from two standard terms, the future value of a lump sum and of an annuity, and the page fetches no market or product data at any point.
That last part matters: the annual return is not a quote, it is a figure you type, and it moves the result more than anything else on screen. Three habits keep the output honest.
- Run it twice: once at the return you hope for, once two points lower. The gap between the balances shows how much of the projection rests on the assumption rather than on your deposits.
- Read the split, not the total: the results separate what you contributed from what growth added. Only the first is a decision you make again next month.
- Discount for inflation: an inflation assumption restates the balance in today’s prices, because a large number thirty years out does not buy what it buys now.
Tax, fees and currency conversion are excluded, as is any income you spend instead of reinvesting. The page is arithmetic on your assumptions: it recommends no product, fund or strategy, and it is not advice about whether to invest.
Which calculator to open
- Savings, investments and working back from a target: compound interest calculator.
- A discount, a percentage change, or what percent one number is of another: percentage calculator.
- The tax and the total on a US purchase, by state: sales tax calculator. Local rates differ by city and county, so add yours if you know it.
Currency and privacy
In the compound interest calculator, amounts are plain numbers with thousands separators and no currency symbol, so read them as dollars, pounds or euros; the arithmetic does not care, as long as every box uses the same currency.
The calculation runs in your browser and there is no account. The compound interest calculator keeps your last five sets of inputs in this browser so you can restore them, and you can delete them from the list on the page. Your figures are not written into the address bar, so a copied link carries the tool and not your numbers.
Common questions
Does the sales tax calculator include city and county tax?
It starts from the state rate for all 50 states and DC. Individual city and county rates are not built in: the page shows the average local rate for the state as a guide, and there is a box for your own local rate if you know it. Sales tax calculator
Where does the compound interest calculator get its rate of return?
It does not get one. The annual return and the inflation rate are assumptions you type in, and no market, index or product data is fetched. Run the same projection again at a lower return to see how much of the result rests on that assumption. Compound interest calculator
Is any of this financial advice?
No. Each page runs a standard formula on the figures you enter and recommends no product, fund or strategy. The compound interest projection also excludes tax, fees and currency conversion, so if the decision is a large one it is worth discussing with a qualified adviser in your own country.
Which currency are the compound interest amounts in?
None in particular. Amounts are shown as plain numbers with thousands separators and no currency symbol, so you can read them as dollars, pounds, euros or anything else. Just keep every box in the same currency. Compound interest calculator
Is anything I type stored or sent anywhere?
Nothing is sent to this site: the calculation happens in your browser, and there is no account and no database. The compound interest calculator keeps your last five sets of inputs in this browser so you can restore them, and you can delete them from the list on the page. Your figures are not written into the URL, so a copied link carries the tool and not your numbers. The site also runs a session recording service (Microsoft Clarity): the tool area of every page, input and results, is masked from it. The details are in the privacy policy. Privacy policy