What is compound interest?

Compound interest is interest calculated on both the initial principal and the previously accumulated interest. Unlike simple interest, it grows exponentially over time.

How often should interest compound?

The more frequently interest compounds (daily > monthly > quarterly > annually), the more you earn. Daily compounding yields slightly more than monthly, which is better than annual.

What is the Rule of 72?

Divide 72 by your interest rate to estimate how many years it takes to double your money. At 7%, your money doubles in about 10.3 years.

What is the Rule of 72?

The Rule of 72 is a quick mental shortcut: divide 72 by your annual interest rate to estimate how many years it takes to double your money. At 7%, money doubles in roughly 72 ÷ 7 ≈ 10.3 years. It's not exact but surprisingly accurate for rates between 4–12%.

Does compound interest work against you in debt?

Yes. The same math that grows savings also grows debt. Credit card debt at 20% APR: $5,000 left unpaid grows to over $30,000 in 10 years. The key difference is direction — in savings, time is your ally; in debt, time works against you. Paying off high-interest debt first often beats investing, purely on a risk-adjusted return basis.

複利計算ツール

複利によって資産がどのように成長するかを計算します。

初期金額

毎月の積立額

年利率

期間

年

複利計算頻度

最終残高

$54,915.51

元本$10,000.00

総積立額$24,000.00

入金総額$34,000.00

獲得利息$20,915.51

総リターン61.52%

年 1$13,215.88 ($12,400.00 + $815.88 interest)

年 2$16,664.23 ($14,800.00 + $1,864.23 interest)

年 3$20,361.86 ($17,200.00 + $3,161.86 interest)

年 4$24,326.80 ($19,600.00 + $4,726.80 interest)

年 5$28,578.36 ($22,000.00 + $6,578.36 interest)

年 6$33,137.26 ($24,400.00 + $8,737.26 interest)

年 7$38,025.74 ($26,800.00 + $11,225.74 interest)

年 8$43,267.59 ($29,200.00 + $14,067.59 interest)

年 9$48,888.39 ($31,600.00 + $17,288.39 interest)

年 10$54,915.51 ($34,000.00 + $20,915.51 interest)

At 7.00% annual interest compounded 月次 with $200.00/month contributions, $10,000.00 grows to $54,915.51 in 10 年 — earning $20,915.51 in interest.

もしもシミュレーション

年利率$54,915.51

期間$54,915.51

Starting 10 years earlier typically doubles your final balance. Time beats rate every time.

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Retirement Savings Calculator

See if this growth puts you on track for retirement

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この計算ツールについて

複利とは、元本だけでなく、すでに積み上がった利息にも利息がつく仕組みです。この「利息の利息」効果により、資産は指数関数的に増加します。運用期間が長いほど成長は劇的になり、早期の貯蓄開始が重要とされる理由です。

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よくある質問

複利とは何ですか？

複利とは、元本と過去に積み上がった利息の両方に対して計算される利息です。単利と異なり、時間とともに指数関数的に増加します。

複利の頻度はどのくらいが良いですか？

頻度が高いほど（日次>月次>四半期>年次）収益が増えます。日次複利は月次より若干高い収益をもたらします。

72の法則とは何ですか？

72を利率で割ると、資産が2倍になるまでのおよその年数がわかります。利率7%なら約10.3年で2倍になります。

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Compound Interest vs. Simple Interest — The Difference That Builds (or Costs) You a Fortune

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The Rule of 72 Explained — Mental Math Every Investor Should Know

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