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 savings goal and how much you have already saved.
- Enter how many years you have to reach the goal.
- Enter the interest rate your savings account pays and how often it compounds.
- The result is the monthly deposit needed, made at the end of each month.
計算式
The future value of current savings plus a series of monthly deposits must equal the goal. Solving for the deposit D, where i is the monthly rate and n the number of months:
Goal = P(1 + i)^n + D × ((1 + i)^n − 1) / i
D = (Goal − P(1 + i)^n) × i / ((1 + i)^n − 1)
Example
- Goal $50,000 in 5 years, $5,000 saved, 4% compounded monthly (i ≈ 0.003333, n = 60).
- The current savings grow to 5,000 × 1.2210 ≈ $6,105.
- D = (50,000 − 6,105) × 0.003333 / 0.2210 ≈ $662 per month.
よくある質問
What if my savings already reach the goal?
If your current balance will grow past the goal with interest alone, the required monthly deposit is zero.
Should I count on interest?
Savings rates can change. Using a lower rate than today's gives you a safety margin.
Is this for an emergency fund?
Yes. Set your goal to three to six months of essential expenses, a common guideline.