diff --git a/src/__tests__/templates-branch-coverage.test.ts b/src/__tests__/templates-branch-coverage.test.ts
new file mode 100644
index 0000000..c1c7ed3
--- /dev/null
+++ b/src/__tests__/templates-branch-coverage.test.ts
@@ -0,0 +1,276 @@
+import { describe, it, expect } from "vitest";
+import { renderTemplate, TemplateData } from "../services/templates.js";
+
+describe("Receipt template optional branches", () => {
+  const baseReceipt = {
+    receiptNumber: "R-100",
+    date: "2026-03-01",
+    items: [{ description: "Item", amount: 10 }],
+  };
+
+  it("renders from.address when present", () => {
+    const html = renderTemplate("receipt", {
+      ...baseReceipt,
+      from: { name: "Shop", address: "123 Main St" },
+    } as TemplateData);
+    expect(html).toContain("123 Main St");
+    expect(html).toContain('class="center"');
+  });
+
+  it("omits from.address when absent", () => {
+    const html = renderTemplate("receipt", {
+      ...baseReceipt,
+      from: { name: "Shop" },
+    } as TemplateData);
+    // The "Thank you!" div has class="center", but no address div should exist
+    const addressDivCount = (html.match(/class="center"/g) || []).length;
+    // Only the "Thank you!" div should have class="center", not an address div
+    expect(addressDivCount).toBe(1);
+  });
+
+  it("renders to.name (Customer line) when present", () => {
+    const html = renderTemplate("receipt", {
+      ...baseReceipt,
+      from: { name: "Shop" },
+      to: { name: "John Doe" },
+    } as TemplateData);
+    expect(html).toContain("Customer: John Doe");
+  });
+
+  it("omits Customer line when to.name is absent", () => {
+    const html = renderTemplate("receipt", {
+      ...baseReceipt,
+      from: { name: "Shop" },
+    } as TemplateData);
+    expect(html).not.toContain("Customer:");
+  });
+
+  it("renders paymentMethod when present", () => {
+    const html = renderTemplate("receipt", {
+      ...baseReceipt,
+      from: { name: "Shop" },
+      paymentMethod: "Credit Card",
+    } as TemplateData);
+    expect(html).toContain("Paid via: Credit Card");
+  });
+
+  it("omits paymentMethod when absent", () => {
+    const html = renderTemplate("receipt", {
+      ...baseReceipt,
+      from: { name: "Shop" },
+    } as TemplateData);
+    expect(html).not.toContain("Paid via:");
+  });
+});
+
+describe("Receipt template fallback branches", () => {
+  it("renders without from (falls back to empty object)", () => {
+    const html = renderTemplate("receipt", {
+      receiptNumber: "R-200",
+      date: "2026-03-01",
+      items: [{ description: "Item", amount: 5 }],
+    } as TemplateData);
+    expect(html).toContain("R-200");
+    expect(html).toContain("€5.00");
+  });
+
+  it("renders without to (falls back to empty object)", () => {
+    const html = renderTemplate("receipt", {
+      receiptNumber: "R-201",
+      date: "2026-03-01",
+      from: { name: "Shop" },
+      items: [{ description: "Item", amount: 5 }],
+    } as TemplateData);
+    expect(html).not.toContain("Customer:");
+  });
+
+  it("renders with custom currency", () => {
+    const html = renderTemplate("receipt", {
+      receiptNumber: "R-202",
+      date: "2026-03-01",
+      from: { name: "Shop" },
+      currency: "$",
+      items: [{ description: "Item", amount: 7 }],
+    } as TemplateData);
+    expect(html).toContain("$7.00");
+  });
+
+  it("renders with empty items array", () => {
+    const html = renderTemplate("receipt", {
+      receiptNumber: "R-203",
+      date: "2026-03-01",
+      from: { name: "Shop" },
+    } as TemplateData);
+    expect(html).toContain("€0.00");
+  });
+});
+
+describe("Invoice template fallback branches", () => {
+  it("renders without from (falls back to empty object)", () => {
+    const html = renderTemplate("invoice", {
+      invoiceNumber: "INV-300",
+      date: "2026-03-01",
+      to: { name: "Buyer" },
+      items: [{ description: "Widget", quantity: 1, unitPrice: 10 }],
+    } as TemplateData);
+    expect(html).toContain("INV-300");
+  });
+
+  it("renders without to (falls back to empty object)", () => {
+    const html = renderTemplate("invoice", {
+      invoiceNumber: "INV-301",
+      date: "2026-03-01",
+      from: { name: "Seller" },
+      items: [{ description: "Widget", quantity: 1, unitPrice: 10 }],
+    } as TemplateData);
+    expect(html).toContain("INV-301");
+  });
+});
+
+describe("Invoice item default values", () => {
+  it("defaults quantity to 1 when missing", () => {
+    const html = renderTemplate("invoice", {
+      invoiceNumber: "INV-400",
+      date: "2026-03-01",
+      from: { name: "S" }, to: { name: "B" },
+      items: [{ description: "Widget", unitPrice: 10 }],
+    } as TemplateData);
+    expect(html).toContain("€10.00"); // 1 * 10
+  });
+
+  it("defaults unitPrice to 0 when missing", () => {
+    const html = renderTemplate("invoice", {
+      invoiceNumber: "INV-401",
+      date: "2026-03-01",
+      from: { name: "S" }, to: { name: "B" },
+      items: [{ description: "Free item", quantity: 2 }],
+    } as TemplateData);
+    expect(html).toContain("€0.00");
+  });
+
+  it("defaults items to empty array when missing", () => {
+    const html = renderTemplate("invoice", {
+      invoiceNumber: "INV-402",
+      date: "2026-03-01",
+      from: { name: "S" }, to: { name: "B" },
+    } as TemplateData);
+    expect(html).toContain("€0.00");
+  });
+});
+
+describe("Receipt item default values", () => {
+  it("defaults amount to 0 when missing/invalid", () => {
+    const html = renderTemplate("receipt", {
+      receiptNumber: "R-300",
+      date: "2026-03-01",
+      from: { name: "Shop" },
+      items: [{ description: "Bad item", amount: "not-a-number" }],
+    } as unknown as TemplateData);
+    expect(html).toContain("€0.00");
+  });
+});
+
+describe("Invoice template optional branches", () => {
+  const baseInvoice = {
+    invoiceNumber: "INV-100",
+    date: "2026-03-01",
+    from: { name: "Seller" },
+    to: { name: "Buyer" },
+    items: [{ description: "Widget", quantity: 1, unitPrice: 10 }],
+  };
+
+  it("renders dueDate when present", () => {
+    const html = renderTemplate("invoice", {
+      ...baseInvoice,
+      dueDate: "2026-04-01",
+    } as TemplateData);
+    expect(html).toContain("Due: 2026-04-01");
+  });
+
+  it("omits dueDate when absent", () => {
+    const html = renderTemplate("invoice", baseInvoice as TemplateData);
+    expect(html).not.toContain("Due:");
+  });
+
+  it("renders from.address when present", () => {
+    const html = renderTemplate("invoice", {
+      ...baseInvoice,
+      from: { name: "Seller", address: "456 Elm St\nSuite 2" },
+    } as TemplateData);
+    expect(html).toContain("456 Elm St<br>Suite 2");
+  });
+
+  it("omits from.address when absent", () => {
+    const html = renderTemplate("invoice", baseInvoice as TemplateData);
+    // from section should have name but no address paragraph
+    const fromSection = html.split('<h3>From</h3>')[1]?.split('<h3>To</h3>')[0];
+    expect(fromSection).not.toContain('<p>456');
+  });
+
+  it("renders from.email when present", () => {
+    const html = renderTemplate("invoice", {
+      ...baseInvoice,
+      from: { name: "Seller", email: "seller@test.com" },
+    } as TemplateData);
+    expect(html).toContain("seller@test.com");
+  });
+
+  it("renders from.vatId when present", () => {
+    const html = renderTemplate("invoice", {
+      ...baseInvoice,
+      from: { name: "Seller", vatId: "ATU12345678" },
+    } as TemplateData);
+    expect(html).toContain("VAT: ATU12345678");
+  });
+
+  it("renders to.address when present", () => {
+    const html = renderTemplate("invoice", {
+      ...baseInvoice,
+      to: { name: "Buyer", address: "789 Oak Ave" },
+    } as TemplateData);
+    expect(html).toContain("789 Oak Ave");
+  });
+
+  it("renders to.email when present", () => {
+    const html = renderTemplate("invoice", {
+      ...baseInvoice,
+      to: { name: "Buyer", email: "buyer@test.com" },
+    } as TemplateData);
+    expect(html).toContain("buyer@test.com");
+  });
+
+  it("renders to.vatId when present", () => {
+    const html = renderTemplate("invoice", {
+      ...baseInvoice,
+      to: { name: "Buyer", vatId: "DE999999999" },
+    } as TemplateData);
+    expect(html).toContain("VAT: DE999999999");
+  });
+
+  it("renders paymentDetails when present", () => {
+    const html = renderTemplate("invoice", {
+      ...baseInvoice,
+      paymentDetails: "IBAN: AT123456\nBIC: BKAUATWW",
+    } as TemplateData);
+    expect(html).toContain("Payment Details");
+    expect(html).toContain("IBAN: AT123456<br>BIC: BKAUATWW");
+  });
+
+  it("omits paymentDetails when absent", () => {
+    const html = renderTemplate("invoice", baseInvoice as TemplateData);
+    expect(html).not.toContain("Payment Details");
+  });
+
+  it("renders notes when present", () => {
+    const html = renderTemplate("invoice", {
+      ...baseInvoice,
+      notes: "Thank you for your business",
+    } as TemplateData);
+    expect(html).toContain("Thank you for your business");
+  });
+
+  it("omits notes when absent", () => {
+    const html = renderTemplate("invoice", baseInvoice as TemplateData);
+    expect(html).not.toContain("<strong>Notes</strong>");
+  });
+});