Compound Interest Calculator
Forecast investment growth, regular deposit accumulation, and compounding returns over any time horizon.
A deposit at the start of a period earns interest for that whole period, so it ends slightly higher.
Milestone Progression
Annual Accruals| Year | Total Deposited | Interest Earned | Ending Balance |
|---|
The Compounding Formula
Calculated using the standard discrete formula A = P(1 + r/n)^(nt) + PMT × [((1 + r/n)^(nt) - 1) / (r/n)], with each deposit made at the end of its period. Choose "Start of each period" to multiply the deposit part by (1 + r/n) instead. The rate can be anything from 0% to 30% and the horizon up to 50 years; type it in the box if it is beyond the slider.
Frequency Impact
More frequent compounding (such as weekly or fortnightly) puts earned interest back into the principal pool faster, compounding returns at an accelerated rate over decades.
Private Financial Modeling
Your portfolio size, savings rate, and timeline never leave your machine. Calculations execute entirely client-side without analytical tracking.
Frequently Asked Questions
How is compound interest calculated?▼
Interest is added to the balance at each compounding period, and the next period earns interest on the new, larger balance. The core formula is A = P(1 + r/n)^(nt), where P is the starting amount, r the annual rate, n the compounding periods per year and t the number of years.
Does it matter whether deposits are made at the start or end of the period?▼
Yes. A deposit made at the start of each period earns interest for one extra period. Use the timing choice to match how you actually contribute; the default is the end of each period.
Can I use a 0% interest rate?▼
Yes. At 0% the balance simply grows by your contributions, which is a useful baseline to see how much of a final balance is interest.
Why are there limits on the rate and the number of years?▼
The inputs are limited to 30% a year and 50 years so that results stay realistic. If you type a value outside the limits, it is adjusted and a note tells you.
Are the results a guarantee or financial advice?▼
No. This is a projection from the numbers you enter. Real returns vary, and fees, taxes and inflation are not included.
Is my data sent to a server?▼
No. The calculator runs entirely in your browser, so nothing you enter is uploaded, stored or tracked. Once the page has loaded it keeps working without a connection.