Formula Help - Tiered Annual Commission Structure by Monthly Payout

Thank you for responding! The formula you suggested only applies to individual months that fall into the Rate% Table. I am trying to get a rolling Rate, especially difficult for me to formulate when a rate threshold is crossed.

Example:
July = $50K sold, Commission would be $5,000
August = $75K sold (but $125K Total Annually) Commission would be ($50K at 10%) $5,000 + ($25K at 11%) $2,750 = Total August Commission $7,750
September = $10K Sold ($135K Annual) so this is paid on an 11% Rate = Commission would be $1100
October = $75K Sold ($210K Annual) Commission would be ($65K at 11%) $7,150 + ($10K at 21%) $2,100 = Total October Commission $9,250
November = $10K Sold ($220K Annual) so this is paid on a 21% Rate = Commission would be $2,100

and so on.....

Do you have a formula that would calculate this properly?

I added the document with your formula inserted in Row 14 for reference.
Your formula returns : 5000, 7500, 1000, 7500, 1000....
It should return: 5000,7750,1100,9250,2100....