#nickdnk_unexpected

1 messages · Page 1 of 1 (latest)

errant breachBOT
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shadow wave
crimson geyser
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But I tried both of those methods

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Im no longer at my computer so I can’t see the invoice you posted, but you can see the sub ID I provided

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Regardless of how you round it internally, presenting 25% of 153.85 on the invoice as 38.47 isn’t right. Only ceiling rounding would give that result, which seems odd.

shadow wave
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The reason why I need to confirm is that the invoice I shared shows 38.96 EUR in tax.

crimson geyser
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Uhh

shadow wave
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So it seems like we're looking at 2 different invoices and I need to be help me confirm the one you're seeing

crimson geyser
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I will get back to you in like 10-15 minutes

shadow wave
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I'm trying to help, and if we're looking at different things it is not going to be productive

crimson geyser
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Sure

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I just don’t know where you got that from the sub I linked

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Im on the phone right now, I’ll message you in a bit

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Maybe I was looking at upcoming invoice for the sub

shadow wave
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Sounds good!

crimson geyser
shadow wave
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The first item for -42.19x.25 = -10.55 (10.5775)
The next item for 175x.25 = 43.75 (43.75)
The next item for 5.50x.25 = 1.38 (1.375)
The next item for 17.50x.25= 4.38 (3.75)

You all those and get 38.96: in_1RrEoXL7ilRdQXxEbYWh3kyc as expected.

Oh, you're looking in the Dashboard for the upcoming invoice?

crimson geyser
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im looking at this yes

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I did what you did here for that one and I get 38.46. If I don't round them off at all to ints before I sum them, I get 38.4615

# 
public static function calculateTaxForValueWithDiscount(float $cost, float $taxPercentage, float $discount): float
    {

        if (!$taxPercentage) {
            return 0;
        }

        $discount = ($discount ? $cost * ($discount / 100) : 0);

        return ($taxPercentage / 100) * ($cost - $discount);

    }

and then:

$user = SomeClass::calculateTaxForValueWithDiscount(1750, 25, 22.3);

$members = SomeClass::calculateTaxForValueWithDiscount(550, 25, 22.3);

$identity = SomeClass::calculateTaxForValueWithDiscount(17500, 25, 22.3);

echo $user + $members + $identity; // = 3846.15
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I've tried in various different ways and I can't seem to get 38.47 except if I essentially ceil the result

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am I just bad at math?

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If I round off every line I still get 38.4625

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Just to clarify that I tried both

shadow wave
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The discount is applied to the entire Invoice. When they do that, apply the discount on each Invoice Items. We calculated a one-cent difference in the amount of the applied discount for this specific Invoice Item.

Let me try to break down the math manually

crimson geyser
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Yeah I don’t know how to convert that explanation to code

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I guess I could try calculating the non-rounded cost (with discount) for each item, sum that instead of the rounded total, then use that for the tax basis

errant breachBOT
chrome notch
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Hi there 👋 jumping in as my teammate needs to step away soon. Out of curiosity, if you create a preivew of the next Invoice for this Subscription via the API, does it show the same tax amounts as the dashboard?

crimson geyser
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I didn’t try that

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I would assume those would be the same

chrome notch
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I'd hope so, but I trust it more if I can see it 😅 we don't know the dashboard super well in this forum, but I know it enough to know it doesn't always do things the same way.

So I'm trying to understand whether this is possibly a dashboard bug, or a math mixup somewhere. And the generation of the preview Invoice will give us more detailed views into the breakdowns of discounts and tax amounts per line item, which may give us the insight we're missing.

crimson geyser
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Alright. Let me see it I can do this

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pretty big response

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can't post it here

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you have to download it

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but it also says 38.47

chrome notch
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Yup, and all the individual tax_amounts in the lines array sum up to that number 🤔

crimson geyser
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Am I crazy or are you also confused?

chrome notch
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I'm still doing the math

crimson geyser
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alright

chrome notch
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Hm, the numbers are all adding up for me when I used the tax_amounts.taxable_amounts from each line, and round at the line item level.

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Are the line item amounts you're calculating after discounts aligning with those taxable_amounts?

crimson geyser
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let me check

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They don't. If I do:
$discount = round($discount ? $cost * ($discount / 100) : 0);

I get 3903 discount amount for 17500, where the API says 3902. The unrounded value is 3902.5, so it seems I need to use a different rounding for that

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RoundingMode::HalfTowardsZero seems to make it correct

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but that's not the PHP default

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and with so many to choose from and so many places where you can do the round-off, it becomes very hard to figure out

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Wrong for the 550 value though, that gives me 123 and not 122 like the API, with that rounding mode

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RoundingMode::TowardsZero gives both 122 and 3902 for the discounts, final result being 3846.5 which would round to 3847.

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550 giving 122 and 17500 giving 3902, that is

chrome notch
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How pressing is this? I have a suspicion of what is going on here, but it will take me a while to do the math and confirm.

crimson geyser
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Not at all, just confused

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Just some working code here:

public static function calculateTaxForValueWithDiscount(float $cost, float $taxPercentage, float $discount): float
    {

        if (!$taxPercentage) {
            return 0;
        }

        $discount = round($discount ? $cost * ($discount / 100) : 0, mode:RoundingMode::TowardsZero); // this rounding mode being the only one that seems to get it right in all 3 cases

        return ($taxPercentage / 100) * ($cost - $discount);

    }

and then:

$user = SomeClass::calculateTaxForValueWithDiscount(1750, 25, 22.3);

$members = SomeClass::calculateTaxForValueWithDiscount(550, 25, 22.3);

$identity = SomeClass::calculateTaxForValueWithDiscount(17500, 25, 22.3);

echo round($user + $members + $identity); // = 3847
chrome notch
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I know the math for splitting fixed amount discounts applied to the Invoice level, across all of the Invoice Items is very finicky and not as intuitive as it feels like it should (with good reason, but that I only barely grasp).

I am not sure offhand if same logic is used for percentage based discounts like you used. I can step through the math and see if that lines up, but it will take me a bit.

crimson geyser
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but if I used RoundingMode::TowardsZero when I add them all together, I'd be at 3846 again

chrome notch
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With that approach, we essentially know the total amount of the discount for the Invoice, then we split that amount across the items. That doesn't always line up to the same amount as if you just calculated the percentages directly, and the remainder of one invoice item impacts the calculations for the next.

crimson geyser
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Yea you can take your time, it's not really super important, I was just trying to get it right for our case

chrome notch
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Cool, let me try to burn down some of these other threads, and I'll circle back when I can do that math with focus to make sure I don't mix things up.

crimson geyser
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No problem

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Gonna play some Hitman with my girlfriend, just @ me

chrome notch
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Will do!

chrome notch
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(I am working on ending up just as confused 😅 )

errant breachBOT
chrome notch
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@crimson geyser sorry, I can't make sense of this either. This isn't lining up with any of the ways I know we round things (unless I'm mixing up my math and haven't spotted that yet).

It almost looks like we always round down, maybe until there is enough discount remainder to round up, but not in the way I'm used to seeing. I think this should be turned into a support case so we can 1) confirm with the right folks internally whether this calculation is as expected and 2) push to get any funky math going on there documented so this is easier to make sense of in the future.
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crimson geyser
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Alright, I guess you’ll take over from here then.