Make sure you want to apply the commission to the entire amount and not
just the marginal amount. For example, let's say your commission
structure is

< $1,000,000 = 1% commission
$1,000,000-$2,000,000 = 2% commission
$3,000,000 = 3% commission

In the formula you're doing, if the salesman sold $999,999, his
commission would be $9,999.99.

But if he sold $1,000,001, his commission would be $20,000.00.

Two extra dollars in sales brought $10,000.01 in commissions!!!!!

The way this should be done is up to $1,000,000 is 1%, every dollar
AFTER $1,000,000 is 2%, etc.

That way $1,000,001 in sales would give $1,000,000 x 1% + $1 x 2%, for
a total of $10,000.02.

That said, I've seen this commission structure many, many times, where
one additional dollar in sales bumps up your commission percentage ALL
THE WAY BACK TO ZERO. I'm amazed companies do something so illogical,
but oh well.

Also, this can e done with a table & formulas instead of having to use
VBA. You're destroying an anthill with a rocket launcher here....