It takes ten years for a $100 monthly bank deposit to amount to $15,528.23 when invested at 5% interest compounded monthly

1 answer

To verify whether a monthly deposit of $100 at an interest rate of 5%, compounded monthly, will amount to $15,528.23 over 10 years, we can use the future value of an annuity formula:

\[ FV = P \times \frac{(1 + r)^n - 1}{r} \]

Where:

  • \( FV \) = future value of the annuity
  • \( P \) = amount of each deposit (payment)
  • \( r \) = interest rate per period
  • \( n \) = total number of payments

For this scenario:

  • \( P = 100 \) (monthly deposit)
  • Annual interest rate = 5%, so monthly interest rate \( r = \frac{0.05}{12} = \frac{0.05}{12} \approx 0.0041667 \)
  • Total payments over 10 years = \( 10 \times 12 = 120 \)

Substituting the values:

\[ FV = 100 \times \frac{(1 + 0.0041667)^{120} - 1}{0.0041667} \]

Calculating \( (1 + 0.0041667)^{120} \):

\[ (1 + 0.0041667)^{120} \approx 1.647009 \]

Now, substituting this value back into the formula:

\[ FV = 100 \times \frac{1.647009 - 1}{0.0041667} \]

Calculating:

\[ \frac{1.647009 - 1}{0.0041667} = \frac{0.647009}{0.0041667} \approx 155.28 \]

\[ FV \approx 100 \times 155.28 \approx 15528 \]

Thus, the future value \( FV \) is approximately $15,528, which confirms your statement. Therefore, a $100 monthly deposit at an interest rate of 5% compounded monthly will indeed amount to $15,528.23 after 10 years.