Calculating Discount - Buy Two Get Another Free

I am scratching my head on this...its not as simple as it first appears.

I can easily calculate if there are three of the same item in the cart and then discount (in cash) the amount equal to the cost of one of them.

For example: Say Item price is 30.00. The user sticks three (3 x 30.00 = 90.00) in the cart and because then the quantity threshold for this item has been met, it shows in the discounts 30.00...easy so far!

Now, my client has asked me, "what if a customer puts six in the cart", it should give a discount totalling 60.00.

What the client is saying is that "for every 3 of the same item in the cart, it should show a 30.00 discount"

So, if there was (say) 4 or five items of the same in the cart, it would only show a 30.00. Once it hits 6, then show 60.00 discount...again it remains at 60.00 if the customer adds 7 or 8 unless the customer updates the quantity to 9...and so on and so on?

There's probably an easy way to do this...anyone out there got a tip or hint?

Thanks in advance.

I think you can do this with a custom column in the cart.

You can create a column like: QuantityDiscount = floor([Quantity]/3) * [Price]

Then create the rule to discount the total of the QuantityDiscount column instead of just discounting the 30.00.

They say you should always sleep on it. I woke this morning and realised I was approaching this in completely the wrong way. It was never a programatic code issue, it was a math issue, and so...

([Quantity] > [DiscountUnitThreshold]) ? (floor([Quantity] / ([DiscountUnitThreshold] + 1))) * [DiscountAmount] : ''

I guess its another way of doing what Ray has done with my own columns.

Thanks Ray...I will take a look at your method...it might be a little less code :-)

You don't need the check in the front or the +1 I don't think. This might be right:

([DiscountUnitThreshold] > 0) ? (floor([Quantity] / ([DiscountUnitThreshold]))) * [DiscountAmount] : 0

The check at the front is to check if the quantity ordered is > than the DiscountUnitThreshold (which is variable for each product)...and yes, I updated the code slightly and I did not need to include +1.

Thanks for your replies Ray!

Yes, but the math will result in zero if the quantity is < the DiscountUnitThreshold anyway, so no need to check. You just need to check that the DiscountUnitThreshold is not zero since you can't divide by zero.