Interest Calc and print

[hanes]

I am trying to calculate the interest rate earned for every year up until retirement age (65) including the interest rate the user inputs.

 

ex: 

Current_age = 30

Interest rate = 6.0

Contribute_amout = 500

Calculates it annually or monthly

 

I want to display the Total amount earned for every year up until retirement age

ex: 

year 1 earned $530.00

year 2 earned $1091.80

year 3 earned $1187.31

etc...

[Barand]

try

 

$age = 30;
$capital = 500;
$rate = 0.06;

echo '<pre>';
printf('%3s | %10s | %10s<br>', 'Age', 'interest', 'capital');
for ($y=$age+1; $y<=65; $y++) {
    $interest = $capital*$rate;
    $capital += $interest;
    printf('%3d | %10.2f | %10.2f<br>', $y, $interest, $capital);
}

[hanes]

 

try

 

$age = 30;
$capital = 500;
$rate = 0.06;

echo '<pre>';
printf('%3s | %10s | %10s<br>', 'Age', 'interest', 'capital');
for ($y=$age+1; $y<=65; $y++) {
    $interest = $capital*$rate;
    $capital += $interest;
    printf('%3d | %10.2f | %10.2f<br>', $y, $interest, $capital);
}

interest is seems not to be calculating the right initial amount. The result should look something like this. I cant seem to figure out the right formula.

 

 

Year Contribution Amount Interest Earned Account Total

1   $500.00   $30.00     $530.00

2   $500.00   $61.80     $1,091.80

3   $500.00   $95.51     $1,687.31

4   $500.00   $131.24   $2,318.55

5   $500.00   $169.11   $2,987.66

Edited March 18, 2013 by hanes

[davidannis]

Looks like you want to add the same amount each year. A trivial change to Barand's program:

$age = 30;
$contribution = 500;
$rate = 0.06;

echo '<pre>';
printf('%3s | %10s | %10s<br>', 'Age', 'interest', 'capital');
for ($y=$age+1; $y<=65; $y++) {
    $capital += $contribution;
    $interest = $capital*$rate;
    $capital += $interest;
    printf('%3d | %10.2f | %10.2f<br>', $y, $interest, $capital);
}

produces the following output:

Age |   interest |    capital
 31 |      30.00 |     530.00
 32 |      61.80 |    1091.80
 33 |      95.51 |    1687.31
 34 |     131.24 |    2318.55
 35 |     169.11 |    2987.66
...

[hanes]

Perfect, except for the fact that it calculates it annually. What would the difference be if it was monthly?

[Barand]

The result should look something like this. I cant seem to figure out the right formula.

 

 

Year Contribution Amount Interest Earned Account Total

1   $500.00   $30.00     $530.00

2   $500.00   $61.80     $1,091.80

3   $500.00   $95.51     $1,687.31

4   $500.00   $131.24   $2,318.55

5   $500.00   $169.11   $2,987.66

 

I was showing annual interest, yours is cumulative interest. Try

 

$age = 30;
$capital = 500;
$rate = 0.06;
$cumulative = 0;
echo '<pre>';
printf('%3s | %10s | %10s | %10s<br>', 'Age', 'interest', 'Accum', 'capital');
for ($y=$age+1; $y<=65; $y++) {
    $interest = $capital*$rate;
    $cumulative += $interest;
    $capital += $interest;
    printf('%3d | %10.2f | %10.2f | %10.2f<br>', $y, $interest, $cumulative,$capital);
}