72の法則
投資が2倍になるのにかかる時間を計算します。
入力
2倍になる年数
2倍達成年 2036
72を年間利回りで割ると、投資が2倍になるまでの予想年数がわかります。逆に目標年数で割ると、必要な年間利回りが求められます。
2倍成長タイムライン
@ 7% 年間利回り
資産別比較
インフレの影響
72の法則はインフレが購買力をどれほど速く侵食するかも示します。年率3%のインフレでは、物価はわずか24年で2倍になります。
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Using the Rule of 72 to Estimate Doubling Time
概要
The Rule of 72 is a quick mental shortcut for how long it takes an investment to double at a fixed annual return: just divide 72 by the rate. It is remarkably accurate for typical rates and great for sanity-checking growth without a spreadsheet. This calculator applies it instantly, and also works in reverse to find the rate needed to double in a given time.
使い方（ステップ）
- 1
Enter the annual rate
The expected yearly return or interest rate as a percentage.
- 2
Read the doubling time
The tool divides 72 by the rate to estimate years to double.
- 3
Or solve for the rate
Enter a target number of years to see what annual rate doubles your money in that time.
仕組み
Years to double ≈ 72 ÷ annual interest rate (as a percent). At 8%, money doubles in about 9 years; at 6%, about 12 years. The 72 works because it closely approximates the exact logarithmic doubling formula for rates between roughly 4% and 15%. To find the required rate instead, divide 72 by the number of years you have.
こんなときに使う
Quickly estimating how fast savings will grow. Comparing the long-term impact of different return rates. Showing how inflation erodes purchasing power (how fast prices double).
よくある質問
Very close for rates between about 4% and 15%. At higher or lower rates the approximation drifts slightly from the exact figure, but it remains a useful estimate.
注意事項
The Rule of 72 is a rough mental-math approximation, not investment advice. Real returns are not fixed and are not guaranteed — consult a licensed financial advisor before making investment decisions.