The compound interest formula is: 
Where:
A is the amount you will have.
P is the money you are investing.
r: is the interest rate (in decimals)
n: number of times the interest is compounded per year
t: time (in years)
The first thing is converting the rate from percentage to decimal:
Since the interest is compounded every month and a year has 12 months n=12.
Now we can replace the values in our formula:
We can simplify the exponents to get:
Finally, we can use our calculator to get 288463.33
After 18 your balance in your bank account will be $288463.33
Where:
A is the amount you will have.
P is the money you are investing.
r: is the interest rate (in decimals)
n: number of times the interest is compounded per year
t: time (in years)
The first thing is converting the rate from percentage to decimal:
Since the interest is compounded every month and a year has 12 months n=12.
Now we can replace the values in our formula:
We can simplify the exponents to get:
Finally, we can use our calculator to get 288463.33
After 18 your balance in your bank account will be $288463.33