In D1 enter the Initial value:
$10,000.00

In C1 enter the sales commision:
$900.00

In A1 the current value:
=D1-C1 which will show:
$9,100.00

Use the rest of column A to record the current value as time goes on.

Finally in B1 enter:
=IF(A1/$D$1<1,A1/$D$1,TEXT(A1/$D$1,"0.00%") & " broke even")
and copy down the column.

Here is a sample of what will may see:

$9,100.00     91.00%      $900.00      $10,000.00
$9,282.00     92.82%       
$9,467.64     94.68%       
$9,656.99     96.57%       
$9,850.13     98.50%       
$10,047.14  100.47% broke even       
$10,248.08  102.48% broke even       
$10,453.04  104.53% broke even       
$10,662.10  106.62% broke even       
$10,875.34  108.75% broke even       
$11,092.85  110.93% broke even       
$11,314.71  113.15% broke even       
$11,541.00  115.41% broke even       
$11,771.82  117.72% broke even