Compound Interest Calculator
Project investment growth with contributions and compounding.
How to use
- Enter the initial principal and the monthly contribution (at least one must be greater than 0). Contributions are treated as deposits at the end of each month.
- Fill in the annual rate (%), the term in years (decimals allowed) and pick the compounding frequency: yearly, monthly or daily.
- Results update as you type: final balance, total invested, interest earned and the growth multiple.
- The "year-by-year milestones" table below lists the balance at each full year (up to 10 rows) so you can watch compounding accelerate.
- The currency is whatever you use (yuan, dollars, etc.) — the tool only applies the math and ignores inflation, fees and taxes.
FAQ
Which formulas are used?
The principal grows as P × (1 + r/n)^(n×t). Monthly contributions are converted to a monthly rate i = (1 + r/n)^(n/12) − 1 and accumulate to m × [((1+i)^N − 1) ÷ i], where P is the principal, m the monthly contribution, r the annual rate, n the number of compounding periods per year, t the term in years and N the total number of months. Contributions are assumed to arrive at each month's end and earn no interest that month.
Does the compounding frequency matter much?
Higher frequency means interest is reinvested sooner, which slightly raises the final balance at the same annual rate. At 5% over 10 years the difference between annual and daily compounding is roughly 1% of the balance — just pick the frequency that matches your actual product.
Can the annual rate be 0?
Yes. With a 0% rate the balance never grows, so the final balance equals the total invested and the growth multiple is 1x — handy for pure savings planning. The valid rate range is 0–100%.
Do the results include inflation and taxes?
No. This tool works with nominal returns and ignores inflation, management fees, taxes and interrupted contributions. Real-world results depend on your product's terms; treat the numbers as planning estimates only.