Electirc Bill Formula with Tier based pricing help

I am working on a document that will handle the cost of electricity, but i've hit a road block in trying to calculate the final cost. Here's a very quick explanation:

Column A = kw/h day.

Column F,G,H, & I will indicate the price per kw/h separated into a tier based system.

Column F = The baseline (tier 1) is 12kw/h at $0.15.

Column G = Represents the cost of Tier 2 which is 101-130% of the baseline which means the next 15.6 kw/h above the baseline is charged at $0.19 per kw/h.

Column H = Represents the cost of Tier 3 which is 131-200% of the baseline which is charged at $0.28 per kw/h.

Column I = Represents the cost of Tier 4 which is the any kw/h that is above 200% of the baseline.

So imagine you have 100 kw/h in a day. The first 12 kw/h (baseline) will be charged at $.15 = (12*.15) = $1.80. You will now have 88 kw/h left to calculate. The next 15.6 (call it 15) kw/h (baseline * 130%) will be charged at $0.19. (15*.19) = $2.85 and you will be left with 73 kw/h. the next 24 kw/h (12*200%) will be charged at $0.28. (24*.28) = $6.72 and you will be left with 49 kw/h. The remaining 49 kw/h will be charged the tier 4 price of $0.32 which equals $15.68 (49*0.32).

The total cost of 100 kw/h per day = (15.68+6.72+2.85+1.80) = $27.05. I'm looking for a formula that reflects this kind of math for column L in my spreadsheet. Column L has to be directly related to Column A reflecting the tier based system prices per X amount of kw/h, but one has to remember that the figure in column A (in this case it's approx 75 kw/h) may change at any time. This is why the result has to reflect that possibility that the total number of kw/h in column A may never have to use each tier.

Is something like this possible? I'm assuming it is because the electric company wouldn't be doing this math by hand for millions of people, but rather have a program hence using a formula to compute this. Any help on this matter would be greatly appreciated. Thanks in advance. The spreadsheet is attached below.

You can use this formula in L6:

=ROUND(MAX(MIN(A6,12),0)*F6,2)+ROUND(MAX(MIN(A6-12,15.6),0)*G6,2)+ROUND(MAX(MIN(A6-12-15.6,24),0)*H6,2)+ROUND(MAX(A6-12-15.6-24,0)*I6,2)

then copy down.

Hope this helps.

Pete

dang, you guys didn't waste anytime. You guys are awesome. i will be trying the answers shortly. Thank you guys again, i really appreciate it!