以下のガイドはまだ日本語に翻訳されていないため、英語で表示しています。計算機自体はすべて日本語に対応しています。
この計算機の使い方
- Enter your starting amount and the expected annual interest rate or return.
- Choose how often interest compounds (daily, monthly, quarterly, annually or continuously).
- Add a regular monthly contribution and choose whether it is made at the start or end of each month.
- Set the number of years to see the future value and the growth chart.
計算式
Without contributions, compound interest grows a principal P at nominal rate r compounded n times a year for t years. Continuous compounding uses e. With monthly contributions, each deposit grows for the months remaining; the calculator converts the compounding frequency to an equivalent monthly rate so any combination is consistent.
A = P × (1 + r/n)^(n×t)
A = P × e^(r×t) (continuous)
EAR = (1 + r/n)^n − 1
Example
- $10,000 at 7% compounded monthly for 10 years with no contributions:
- A = 10,000 × (1 + 0.07/12)^120 ≈ $20,096.61.
- Interest earned ≈ $10,096.61, so the money roughly doubles, consistent with the rule of 72 (72 ÷ 7 ≈ 10.3 years).
よくある質問
What is the difference between simple and compound interest?
Simple interest is paid only on the original principal. Compound interest is also paid on interest already earned, so growth accelerates over time.
How much does compounding frequency matter?
More frequent compounding increases the effective annual rate, but the difference between monthly and daily compounding is small. At 7%, monthly compounding gives an EAR of 7.229% and daily gives 7.250%.
What is the rule of 72?
Divide 72 by the annual rate to estimate how many years it takes to double your money. At 6%, money doubles in about 12 years.
Are returns guaranteed?
Savings accounts and CDs pay a stated rate, but investment returns vary from year to year. A constant rate is a simplifying assumption, and taxes and fees are not included.