Compound Interest Calculator
Calculate growth with compound interest
About the Compound Interest Calculator
Compound interest is the reason a modest sum left alone can grow into something substantial — interest earns interest, and the effect snowballs over time. This calculator projects that growth from a principal amount, a rate, and a time horizon, and optionally layers in a monthly deposit so you can model a balance that you keep feeding.
Savers use it to see what a deposit becomes in a decade; investors use it to compare how compounding frequency nudges the outcome. The year-by-year growth table is where it earns its keep, turning an abstract formula into a visible curve so you can watch the gap between contributions and earned interest widen each year.
How to Use the Compound Interest Calculator
- Enter your principal — the starting amount.
- Enter the annual interest rate and the number of years.
- Pick a compounding frequency: daily, monthly, quarterly, or annually.
- Optionally add a monthly deposit to model ongoing contributions.
- Read the final amount, total interest, and total deposits, and expand the year-by-year table to see the growth build.
Why Use ToolForge’s Compound Interest Calculator
- It breaks results into final amount, total deposits, and total interest, so you can see precisely how much growth came from compounding versus from your own money.
- The year-by-year table makes the exponential curve concrete rather than leaving it as a single end figure.
- It supports four compounding frequencies for a lump sum, illustrating how more frequent compounding edges the total higher.
- Calculations are local and instant, so your figures stay on your device.
Frequently Asked Questions
What is compound interest?
Compound interest is interest calculated on both your original principal and the interest already added to it. Unlike simple interest, which is charged only on the principal, compounding means your balance grows on itself, accelerating over time.
How does compounding frequency affect growth?
More frequent compounding credits interest sooner, so it begins earning its own interest earlier. At the same annual rate, daily compounding produces slightly more than annual compounding — the difference is modest over short periods but adds up over many years.
Does adding a monthly deposit change the calculation?
Yes. When you add a monthly deposit, the tool models your contributions as a monthly series growing alongside the principal, which reflects a regular saving habit rather than a single untouched sum. Total deposits are reported separately so you can see your contribution clearly.
What is the rule of 72?
It is a quick mental shortcut: divide 72 by your annual interest rate to estimate the years it takes for money to double. At 6%, that is roughly 12 years. This calculator gives the exact figure, but the rule is a handy sanity check.
