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Pricing Revision and Updates to Deals and Coupon Features

Changes with the Way We Calculate Product Prices, Deals, and Coupons

We recently* modified the way that prices are calculated on Plazko.com for the sake of improved consistency and clarity.

Because we try to maximize the savings that our customers receive, we have to use a complicated algorithm and as a result, sometimes the final prices on orders can be a bit confusing.  For this reason, we also modified the way that we display and breakdown prices and discounts on the shopping cart, checkout, and receipt pages.  Also, there were a few edge cases that would result in bugs in price calculation and failed orders.  These issues have been resolved.

What’s Changed

  • Using multiple coupons no longer results in a failed order
  • Other failed-order related bugs have been fixed (due to fixes in how certain rounding errors are handled)
  • If using paypal to pay, the itemized information sent to paypal is now easier to understand
  • Most discounts are now always calculated on a per product basis, and the discount is rounded up to the nearest cent
    • So, for example:
      • lets say you bought 3 x Item1 for $3.99 each and 5 x Item2 for 5.76 each for a total of 40.77
      • If you had a 10% off coupon, you would get a discount of $4.10, and the total would be reduced to $36.67
      • This is confusing at first because 10% of 40.77 is 4.08 and so you might expect the total to be $36.69; so what’s happening?
      • $3.99 minus 10% is $3.59  and $5.76 minus  10% is $5.18.  So, $3.59 x 3 + $5.18 x 3 = $36.67
      • As a result of calculating per product, you save an additional $0.02
  • The only discounts that are calculated against the subtotal are product-wide flat dollar-amount deals and coupons.  For example, if we have a deal that is”$5 off your entire order of $100 or more” then that $5 discount would not be calculated per product. It would be applied to the overall order total.
  • Shipping discounts are no longer constrained by the item total. Shipping discounts used to be capped at the total item amount (not counting shipping charges) even if that total was less than the stated discount amount.  So a $5 order was not able to have a $6 shipping discount (even if the shipping cost more than that).  Now, the shipping discount is capped at the total shipping price. (So if there is a $5 shipping charge, then the maximum shipping discount is $5 off)
  • The cart, checkout, and invoice screens now all show a breakdown of which products we given which discounts

The Pricing Algorithm

For each invoice line item, let:

  • R = Regular Price
  • S = Plazko’s Every Day Savings
  • D = Deal Discount Amount $
  • C = Coupon Discount Amount $ (except for order-wide (not product specific) flat dollar-amount discounts)
  • F = Order-wide (not product specific) flat dollar-amount coupons and deals
  • P = The Resulting Product Price $


  • C is determined by applying any coupons to the result of R – S – D (in other words, coupons are applied after deals are applied and their value is based on a product’s post-deal price)

So, the price that we will charge (P) is calculated as follows:

P = R – S – D – C – F


As a result of these changes, Plazko.com customers will enjoy increased savings and a more stable ordering experience overall.

Please submit any feedback or suggestions at our contact form.


* As of Revision 3792

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