Incorrect Bundle Discount Calculation

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Apologies if this is not the correct sub-forum, wasn't sure where it fitted.

Using the MBC Bundle app:

Product 1, £4.49
Product 2, £8.99
So total is £13.48

Setting a 10% discount = £12.13

There are 2 settings in the app, display in cart as, 'one product' or 'as multiple products'

With either of the above options, the price on the product detail screen is correct £12.13.

When selecting 'display as one product' all works fine in the cart as well.

When selecting 'display as multiple products' the price on the individual items in the cart is increased buy £0.01, and the overall cost is increased to £12.15.

Now I'm assuming something, somewhere is struggling with the calculation.

10% off £4.49 would come to £4.041, which surely should be rounded down to £4.04? But is instead being rounded up to £4.05.

I've tried MBC support but not received any response - does anyone have any ideas? Is this normal Shopify behaviour?




When the discount is allocated to 3 products, there is a rounding error of $0.01. So the order may appear with an outstanding amount. 

Your discount calculation is not correct. The discount is round down to 2dp. There is no 3dp. If you really want to study the calculation, you can study the Shopify docs.

I've personally studied the discount calculation for days or even weeks just to find out the formula for my bundle app. (You can even see the questions in my threads). But even the official doc is not accurate occasionally.

I think $0.01 is not a big deal, given that the customer already paid you. Just beware that when there are more items, the rounding error will be slightly larger, ie $0.02.

The rounding error comes from the methodology choose here. So it is not avoidable but it can compensated. But more calculations will lead to more errors. The errors may happen again when you update product prices 

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New Member
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The app developers agreed there was an issue and have fixed this now, so we're all good.

The problem was that the price shown in the cart was different than the price shown on the product page, which in my mind isn't going to make the customer feel confident if there are suddenly seeing the different change. I appreciate it's only a very small amount but it didn't look very professional.

Anyway, all resolved now.