Frequently Asked Questions

Compound interest is a method where interest earned is added back to the principal, and subsequent interest is calculated on the new, larger total. Because interest earns interest, your assets grow at an accelerating rate over longer investment periods.

Monthly compounding calculates and adds interest to the principal every month, while annual compounding does so once a year. Since monthly compounding adds interest more frequently, the compound interest effect is greater, resulting in a higher final balance at the same annual rate.

Beginning-of-period adds your deposit to the principal at the start of each period before calculating interest. End-of-period calculates interest first, then adds the deposit. Since beginning-of-period allows your deposit to earn interest sooner, it produces a slightly higher final balance under the same conditions.

Taxed per period means tax is deducted from interest each time it is calculated, at a specified tax rate. This corresponds to the withholding tax on bank deposit interest in Japan (20.315%). Tax-free mode is for tax-advantaged accounts such as NISA.

Most financial institutions use floor (truncation) for interest calculations. If you are unsure, select 'Floor'. Round and Ceil are available for specific financial products that use those methods.

Yes. Click the 'Copy conditions' button at the top of the page to copy the current calculation parameters as a URL to your clipboard. Share that URL with others to reproduce the same results.

This calculator uses standard compound interest formulas. However, actual financial products may have unique calculation rules or fees. Please use the results as a reference only.