Compound Interest Calculator
Simulate the growth of savings or an investment with compound interest, with or without regular contributions, and see the year-by-year evolution. No financial data entered here is sent to a server.
How It Works
Compound interest (“interest on interest”) makes a balance grow at an accelerating rate over time, because the gains from one period themselves generate interest in later periods. This tool simulates that growth period by period (according to the chosen compounding frequency), taking into account an initial principal and regular monthly contributions.
Why does the compounding frequency change the result?
The more often interest is calculated and reinvested (monthly rather than yearly, for example), the earlier and more frequently the “interest on interest” effect occurs, slightly increasing the final balance at the same annual rate. The difference is usually modest but becomes more visible over long periods.
Are monthly contributions added before or after interest is calculated?
In this simulation, interest for each period is calculated on the beginning-of-period balance, and then the period's contribution is added. This is a conservative, commonly used approach for estimating a planned savings plan.
This simulation stays local: your savings amounts are neither stored nor sent to a server.