Compound interest calculator
See how an initial amount plus regular contributions grows when interest earns interest. Choose any compounding frequency from daily to yearly and watch the split between your deposits and the growth on top.
WealthPath Calculator · Compound Interest Calculator · report generated for personal use
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How this calculator works
Your nominal annual rate is converted to an effective annual rate using your chosen compounding frequency, then to an equivalent monthly growth factor so that monthly contributions are handled correctly.
Contributions are applied at the start of each month. The growth chart plots the total balance against the running total of what you have put in, so the gap between the lines is pure compounding.
Reading the result honestly
The interest figure assumes the rate holds every single year. Real returns arrive unevenly, and a poor first decade produces a very different outcome from a poor final one.
Use a rate you would defend to a sceptic, then run it again two points lower. If the plan only works at the higher rate, it is not a plan.
Frequently asked questions
What is compound interest?
Interest earned on your original amount and on the interest already added. Each period's growth becomes part of the base the next period grows on, which is why the curve steepens over time.
Does compounding frequency make much difference?
Less than the rate, the amount or the time. At 8% over twenty years, monthly rather than yearly compounding adds a few percent - useful, but not the thing that decides the outcome.
Can I include monthly contributions?
Yes. Set a monthly figure and the chart separates the running total of your deposits from the growth stacked on top of them.
What is the rule of 72?
Divide 72 by the annual return for an approximate doubling time. At 8% that is about nine years. The stat panel shows the exact figure alongside it.
Is the interest figure guaranteed?
No. It assumes the rate holds every year, which real markets do not do. Use it as a baseline, not a promise.
Worked examples using this calculator
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