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ドルコスト平均法（DCA）計算機

データ開発者数学

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入力

自動処理

出力

クライアント側

DCAプランを入力して、予測を確認してください。

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ガイド

ドルコスト平均法（DCA）計算機

Dollar Cost Averaging is the practice of investing a fixed amount on a regular schedule regardless of market price. This calculator simulates a DCA plan period-by-period, projects the future portfolio value, and compares it to investing the same total amount as a single lump sum. The result is a clear, year-by-year picture of how contributions and compound growth build wealth over time.

使用方法

Enter the amount you plan to invest each period (for example, $500).
Choose how often you contribute — weekly, bi-weekly, monthly, quarterly, or yearly.
Set the investment duration in years (1–60).
Enter your expected annual return rate (the long-term S&P 500 average is roughly 7–10%).
Optionally add an initial lump sum that is invested before the periodic contributions begin.
The summary, comparison, chart, and year-by-year table update automatically.

機能

Period-by-period simulation – Compounds at the exact contribution frequency rather than approximating annually.
DCA vs lump sum comparison – Shows what would have happened if you had invested the entire amount at year zero instead.
Break-even year – Highlights the year your accumulated gains first exceed the total amount you have invested.
Adjustable return rate – Test optimistic, conservative, and pessimistic return assumptions.
Year-by-year growth table – Tracks total invested, portfolio value, gain, and percentage return for every year of the plan.
Interactive chart – Visualizes contributions, the DCA portfolio, and the lump-sum equivalent on one timeline.

 よくある質問

What is dollar cost averaging?

Dollar cost averaging is an investing strategy where the same fixed amount is invested at regular intervals regardless of the asset's current price. Because the same dollar amount buys fewer shares when prices are high and more shares when prices are low, the average cost per share tends to fall over time. It is most often used by retail investors building positions in broad index funds or ETFs through retirement and brokerage accounts.
Is dollar cost averaging better than lump sum investing?

Academic studies (notably from Vanguard) find that in a steadily rising market, investing a lump sum immediately tends to outperform DCA roughly two-thirds of the time because money is exposed to compounding for longer. DCA's advantage is behavioral and risk-related: it reduces the impact of investing right before a downturn and makes it psychologically easier to stay invested through volatile periods.
How does compounding work with regular contributions?

With recurring contributions, each new deposit starts earning returns from the moment it is invested, so earlier contributions accumulate more compound growth than later ones. Mathematically this is the future value of an annuity: FV = PMT * [((1 + r/n)^(n*t) - 1) / (r/n)], where PMT is the periodic contribution, r is the annual rate, n is contributions per year, and t is the number of years.
What return rate should I assume for long-term planning?

Historical long-term equity returns in developed markets have averaged roughly 7-10% per year nominal (before inflation) and 5-7% real (after inflation). Bond-heavy portfolios return less but are less volatile. Most retirement planners model multiple scenarios — for example 5%, 7%, and 9% — to bracket the range of plausible outcomes rather than relying on a single point estimate.