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Compound interest is the effect where not only your invested capital earns interest, but the interest already credited earns interest too. Over many years a savings plan therefore grows not linearly but at an accelerating pace. This calculator shows where your starting capital, together with a monthly contribution at a fixed annual rate, ends up over the chosen term - as a final amount, as a year-by-year table and as a curve in the chart.
The calculation runs entirely locally in your browser, in pure JavaScript - nothing is uploaded and nothing is stored. By default the model compounds monthly and books the contribution at the end of each period - but you can also compound annually, semi-annually, quarterly or daily, and move the deposit to the beginning of the period (then it earns interest for one period longer). From starting capital, monthly rate, annual interest and term you get three key figures: the final balance, the sum of your contributions and the pure interest earned. Change an input and the result, table and chart update instantly.
An honest note: this is a model-based estimate, not financial, tax or investment advice. Taxes (such as capital-gains tax), inflation, fees and fluctuating interest rates are deliberately not included - real-world results will differ. The amounts are shown in euros as an example; the underlying maths applies equally to any currency. For binding statements, talk to a qualified adviser.
Specifications
Specifications
Input formats
Form inputs (no file)
Processing
Locally in your browser (JavaScript)
File upload
None
In 3 steps
Enter the starting capital, monthly contribution, interest rate and term.
Optionally adjust the compounding interval and deposit timing.
Read off the final balance, contributions and interest - with the table and chart.
Change an input; the result updates instantly.
Limitations:A model-based estimate; monthly compounding with end-of-period deposits by default (both selectable). The yearly contribution total is spread evenly across the chosen compounding interval rather than simulated to the exact day. No solve-for-any (only the final balance is computed, not rate/term/contribution backwards). Taxes, inflation, fees and fluctuating rates are not included. The term is limited to 1 to 100 years and the rate to at most 100 % per year. Amounts are in euros as an example - the underlying maths applies to any currency. Not financial, tax or investment advice.
FAQ
Are my inputs uploaded?
No. The calculation runs entirely locally in the browser (pure JavaScript); nothing is sent or stored.
How is compound interest calculated?
With the chosen compounding interval (annually to daily) and the annual rate divided by the number of periods per year; the contribution is booked at the beginning or end of each period depending on the chosen timing.
What does the deposit timing mean?
With "end of period" a deposit first earns interest in the following period - the standard case. With "beginning of period" it already earns interest in the period it is paid into, giving a slightly higher interest yield.
Are taxes and inflation included?
No, deliberately not. Capital-gains tax, inflation and fees are left out, so real-world results will differ.
Is this investment advice?
No. It is a non-binding, model-based estimate. For binding decisions, consult a qualified adviser.
Can I use other currencies?
The amounts are shown in euros as an example; the figures hold unchanged for any other currency.