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fix: calculate tax on discounted amount and add consistent rounding #59

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Merged
darshgupta-wisdm merged 2 commits into from
Apr 16, 2026
Merged

fix: calculate tax on discounted amount and add consistent rounding #59

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3717655
fix: calculate tax on discounted amount and add consistent rounding
darshgupta-wisdm Apr 15, 2026
31fe50a
fix: change taxTotal from const to let for reassignment
darshgupta-wisdm Apr 15, 2026
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7 changes: 4 additions & 3 deletions apps/web/app/(dashboard)/invoices/[id]/edit/edit-invoice-form.tsx
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Original file line number Diff line number Diff line change
Expand Up @@ -377,9 +377,10 @@ export function EditInvoiceForm({
return match?.[1] ? parseFloat(match[1]) : 0;
}, [taxRate, customTaxRate]);

const taxAmount = subtotal * (parsedTaxPercent / 100);
const discountAmount = discountType === 'percent' ? subtotal * (discount / 100) : discount;
const total = Math.max(0, subtotal + taxAmount - discountAmount);
const discountAmount = Math.round((discountType === 'percent' ? subtotal * (discount / 100) : discount) * 100) / 100;
const discountedSubtotal = Math.max(0, Math.round((subtotal - discountAmount) * 100) / 100);
const taxAmount = Math.round(discountedSubtotal * (parsedTaxPercent / 100) * 100) / 100;
const total = Math.max(0, Math.round((discountedSubtotal + taxAmount) * 100) / 100);

// ─── Handlers ────────────────────────────────────────
const [addItemOpen, setAddItemOpen] = useState(false);
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7 changes: 4 additions & 3 deletions apps/web/app/(dashboard)/invoices/new/new-invoice-form.tsx
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Expand Up @@ -408,9 +408,10 @@ export function NewInvoiceForm({
return match?.[1] ? parseFloat(match[1]) : 0;
}, [taxRate, customTaxRate]);

const taxAmount = subtotal * (parsedTaxPercent / 100);
const discountAmount = discountType === 'percent' ? subtotal * (discount / 100) : discount;
const total = Math.max(0, subtotal + taxAmount - discountAmount);
const discountAmount = Math.round((discountType === 'percent' ? subtotal * (discount / 100) : discount) * 100) / 100;
const discountedSubtotal = Math.max(0, Math.round((subtotal - discountAmount) * 100) / 100);
const taxAmount = Math.round(discountedSubtotal * (parsedTaxPercent / 100) * 100) / 100;
const total = Math.max(0, Math.round((discountedSubtotal + taxAmount) * 100) / 100);

// ─── Handlers ────────────────────────────────────────
const [addItemOpen, setAddItemOpen] = useState(false);
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18 changes: 11 additions & 7 deletions apps/web/app/(dashboard)/quotes/[id]/edit/edit-quote-form.tsx
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Expand Up @@ -402,14 +402,18 @@ export default function EditQuoteForm({ quote }: EditQuoteFormProps) {

const tpl = (QUOTE_TEMPLATES[templateName] ?? QUOTE_TEMPLATES.clean) as QuoteTemplate;

const subtotal = lineItems.reduce(
(acc, item) => acc + item.quantity * item.rate,
// Round each line item to match server-side calculation (Bug #178)
const subtotal = Math.round(lineItems.reduce(
(acc, item) => acc + Math.round(item.quantity * item.rate * 100) / 100,
0
);
const discountAmount = discountType === 'percent'
? Math.round(subtotal * (discount / 100) * 100) / 100
: discount;
const total = Math.max(0, subtotal - discountAmount);
) * 100) / 100;
const discountAmount = Math.round((discountType === 'percent'
? subtotal * (discount / 100)
: discount) * 100) / 100;
const effectiveTaxRate = customTaxRate ? parseFloat(customTaxRate) : (taxRate !== 'custom' && taxRate !== '0% - Default' ? parseFloat(taxRate) : 0);
const discountedSubtotal = Math.max(0, Math.round((subtotal - discountAmount) * 100) / 100);
const taxAmount = effectiveTaxRate > 0 ? Math.round(discountedSubtotal * (effectiveTaxRate / 100) * 100) / 100 : 0;
const total = Math.max(0, Math.round((discountedSubtotal + taxAmount) * 100) / 100);

const expirationDate = issueDate
? addDays(issueDate, parseInt(expirationDays) || 30)
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18 changes: 10 additions & 8 deletions apps/web/app/(dashboard)/quotes/new/new-quote-form.tsx
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Original file line number Diff line number Diff line change
Expand Up @@ -299,16 +299,18 @@

const tpl = (QUOTE_TEMPLATES[templateName] ?? QUOTE_TEMPLATES.clean) as QuoteTemplate;

const subtotal = lineItems.reduce(
(acc, item) => acc + item.quantity * item.rate,
// Round each line item to match server-side calculation (Bug #178)
const subtotal = Math.round(lineItems.reduce(
(acc, item) => acc + Math.round(item.quantity * item.rate * 100) / 100,
0
);
const discountAmount = discountType === 'percent'
? Math.round(subtotal * (discount / 100) * 100) / 100
: discount;
) * 100) / 100;
const discountAmount = Math.round((discountType === 'percent'
? subtotal * (discount / 100)
: discount) * 100) / 100;
const effectiveTaxRate = customTaxRate ? parseFloat(customTaxRate) : (taxRate !== 'custom' && taxRate !== '0% - Default' ? parseFloat(taxRate) : 0);
const taxAmount = effectiveTaxRate > 0 ? Math.round((subtotal - discountAmount) * (effectiveTaxRate / 100) * 100) / 100 : 0;
const total = Math.max(0, subtotal - discountAmount + taxAmount);
const discountedSubtotal = Math.max(0, Math.round((subtotal - discountAmount) * 100) / 100);
const taxAmount = effectiveTaxRate > 0 ? Math.round(discountedSubtotal * (effectiveTaxRate / 100) * 100) / 100 : 0;
const total = Math.max(0, Math.round((discountedSubtotal + taxAmount) * 100) / 100);

const expirationDate = issueDate
? addDays(issueDate, parseInt(expirationDays) || 30)
Expand Down Expand Up @@ -447,7 +449,7 @@
} finally {
setPdfGenerating(false);
}
}, [quoteNumber, toast]);

Check warning on line 452 in apps/web/app/(dashboard)/quotes/new/new-quote-form.tsx

View workflow job for this annotation

GitHub Actions / Lint 

React Hook useCallback has an unnecessary dependency: 'toast'. Either exclude it or remove the dependency array. Outer scope values like 'toast' aren't valid dependencies because mutating them doesn't re-render the component

return (
<div className="flex flex-col h-[calc(100vh-64px)]">
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12 changes: 6 additions & 6 deletions apps/web/components/quotes/editor/hooks/useQuoteTotals.ts
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Expand Up @@ -14,20 +14,20 @@ export function useQuoteTotals(blocks: QuoteBlock[] | undefined, taxRate: string
}, [blocks]);

const subtotal = useMemo(() => {
return serviceItems.reduce(
(sum, item) => sum + item.content.quantity * item.content.rate,
return Math.round(serviceItems.reduce(
(sum, item) => sum + Math.round(item.content.quantity * item.content.rate * 100) / 100,
0
);
) * 100) / 100;
}, [serviceItems]);

const globalTaxRate = parseFloat(taxRate) || 0;

const taxAmount = useMemo(() => {
return serviceItems.reduce((sum, item) => {
const lineTotal = item.content.quantity * item.content.rate;
return Math.round(serviceItems.reduce((sum, item) => {
const lineTotal = Math.round(item.content.quantity * item.content.rate * 100) / 100;
const itemTaxRate = item.content.taxRate != null ? item.content.taxRate : globalTaxRate;
return sum + lineTotal * (itemTaxRate / 100);
}, 0);
}, 0) * 100) / 100;
}, [serviceItems, globalTaxRate]);

const total = subtotal + taxAmount;
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10 changes: 8 additions & 2 deletions apps/web/lib/invoices/actions.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -79,11 +79,17 @@ function calculateTotals(
discountAmount = Math.min(discountAmount, subtotal);
discountAmount = Math.round(discountAmount * 100) / 100;

// Tax should apply to the discounted amount, not the full subtotal.
// Proportionally reduce tax by the same ratio as the discount.
if (subtotal > 0 && discountAmount > 0) {
taxTotal = Math.round(taxTotal * ((subtotal - discountAmount) / subtotal) * 100) / 100;
}

return {
subtotal,
taxTotal,
discountAmount,
total: Math.round((subtotal + taxTotal - discountAmount) * 100) / 100,
total: Math.round((subtotal - discountAmount + taxTotal) * 100) / 100,
};
}

Expand Down Expand Up @@ -162,7 +168,7 @@ export async function createInvoice(data: CreateInvoiceData) {
return { success: false, error: 'Discount amount cannot be negative' };
}
// Cap fixed discount at subtotal (calculateTotals also clamps, but reject early for clarity)
const preliminarySubtotal = data.lineItems.reduce((sum, item) => sum + item.quantity * item.rate, 0);
const preliminarySubtotal = data.lineItems.reduce((sum, item) => sum + Math.round(item.quantity * item.rate * 100) / 100, 0);
if (data.discountValue > preliminarySubtotal) {
data.discountValue = preliminarySubtotal;
}
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7 changes: 6 additions & 1 deletion apps/web/lib/quotes/actions.ts
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Expand Up @@ -391,7 +391,7 @@ export async function updateQuote(

// Calculate totals
const subtotal = Math.round((lineItems?.reduce((sum, item) => sum + item.amount, 0) || 0) * 100) / 100;
const taxTotal = Math.round((lineItems?.reduce((sum, item) => sum + item.taxAmount, 0) || 0) * 100) / 100;
let taxTotal = Math.round((lineItems?.reduce((sum, item) => sum + item.taxAmount, 0) || 0) * 100) / 100;

// Bug #123: Validate discount values server-side
const mergedSettings = { ...(existingQuote.settings as Record<string, unknown>), ...data.settings };
Expand All @@ -414,6 +414,11 @@ export async function updateQuote(
} else if (discountType === 'fixed') {
discountAmount = Math.min(discountValue, subtotal);
}

// Tax applies to the discounted amount, not the full subtotal
if (subtotal > 0 && discountAmount > 0) {
taxTotal = Math.round(taxTotal * ((subtotal - discountAmount) / subtotal) * 100) / 100;
}
const total = subtotal - discountAmount + taxTotal;

// Update quote
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5 changes: 5 additions & 0 deletions apps/web/lib/stores/quote-builder-store.ts
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Expand Up @@ -499,6 +499,11 @@ export const useQuoteBuilderStore = create<QuoteBuilderStore>()(
}
}

// Tax applies to the discounted amount, not the full subtotal
if (subtotal > 0 && discountAmount > 0) {
taxTotal = taxTotal * ((subtotal - discountAmount) / subtotal);
}

state.document.totals.subtotal = subtotal;
state.document.totals.discountAmount = discountAmount;
state.document.totals.taxTotal = taxTotal;
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18 changes: 9 additions & 9 deletions packages/database/prisma/seed.ts
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Expand Up @@ -419,42 +419,42 @@ async function main() {

// Add line items (C03 fix: add multiple items per quote for realistic preview)
// Split the total into primary (70%) and secondary (30%) line items
const primaryAmount = Math.round(q.subtotal * 0.7);
const secondaryAmount = q.subtotal - primaryAmount;
const primaryAmount = Math.round(q.subtotal * 0.7 * 100) / 100;
const secondaryAmount = Math.round((q.subtotal - primaryAmount) * 100) / 100;
const primaryQty = Math.max(1, Math.round(q.qty * 0.7));
const secondaryQty = Math.max(1, q.qty - primaryQty);
const primaryRate = Math.round(primaryAmount / primaryQty);
const secondaryRate = Math.round(secondaryAmount / secondaryQty);
const primaryRate = Math.round(primaryAmount / primaryQty * 100) / 100;
const secondaryRate = Math.round(secondaryAmount / secondaryQty * 100) / 100;

await prisma.quoteLineItem.upsert({
where: { id: `quote-item-${quote.id}` },
update: { name: q.itemName, quantity: primaryQty, rate: primaryRate, amount: primaryQty * primaryRate, sortOrder: 0 },
update: { name: q.itemName, quantity: primaryQty, rate: primaryRate, amount: Math.round(primaryQty * primaryRate * 100) / 100, sortOrder: 0 },
create: {
id: `quote-item-${quote.id}`,
quoteId: quote.id,
name: q.itemName,
quantity: primaryQty,
rate: primaryRate,
amount: primaryQty * primaryRate,
amount: Math.round(primaryQty * primaryRate * 100) / 100,
sortOrder: 0,
},
});
await prisma.quoteLineItem.upsert({
where: { id: `quote-item-2-${quote.id}` },
update: { name: 'Project Management', quantity: secondaryQty, rate: secondaryRate, amount: secondaryQty * secondaryRate, sortOrder: 1 },
update: { name: 'Project Management', quantity: secondaryQty, rate: secondaryRate, amount: Math.round(secondaryQty * secondaryRate * 100) / 100, sortOrder: 1 },
create: {
id: `quote-item-2-${quote.id}`,
quoteId: quote.id,
name: 'Project Management',
quantity: secondaryQty,
rate: secondaryRate,
amount: secondaryQty * secondaryRate,
amount: Math.round(secondaryQty * secondaryRate * 100) / 100,
sortOrder: 1,
},
});

// Update totals to match actual line item sums
const actualTotal = (primaryQty * primaryRate) + (secondaryQty * secondaryRate);
const actualTotal = Math.round((primaryQty * primaryRate + secondaryQty * secondaryRate) * 100) / 100;
if (actualTotal !== q.subtotal) {
await prisma.quote.update({
where: { id: quote.id },
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