diff --git a/src/actions/reports.ts b/src/actions/reports.ts
index b7d239c..4f71663 100644
--- a/src/actions/reports.ts
+++ b/src/actions/reports.ts
@@ -84,7 +84,8 @@ export async function deleteReport(
 const DRILL_DOWN_LIMIT = 50;
 
 export async function getDrillDownTransactions(filters: {
-  categoryId?: string;
+  /** A category id, `null` for uncategorized, `undefined` for no category filter. */
+  categoryId?: string | null;
   dateFrom: string;
   dateTo: string;
   type?: "income" | "expense";
@@ -93,7 +94,7 @@ export async function getDrillDownTransactions(filters: {
 
   const page = await withHousehold(householdId, (tx) =>
     getTransactions(householdId, {
-      categoryId: filters.categoryId ?? undefined,
+      categoryId: filters.categoryId,
       dateFrom: filters.dateFrom,
       dateTo: filters.dateTo,
     }, DRILL_DOWN_LIMIT, undefined, tx));
diff --git a/src/components/atoms/spending-chart.tsx b/src/components/atoms/spending-chart.tsx
index 10bfeaf..91303cf 100644
--- a/src/components/atoms/spending-chart.tsx
+++ b/src/components/atoms/spending-chart.tsx
@@ -8,6 +8,8 @@ export interface SpendingChartItem {
   id: string | null;
   name: string;
   value: number;
+  /** Set on the rolled-up "Other" slice this chart builds; not a real category. */
+  synthetic?: boolean;
 }
 
 interface SpendingChartProps {
@@ -18,11 +20,11 @@ interface SpendingChartProps {
 
 // The aggregated "Other" row (built below from categories past the top 8) is
 // not a real category — give it a fixed neutral color instead of cycling back
-// into CHART_COLORS, which would collide with an earlier slice's color.
-// Real uncategorized spend can also carry a null id under a different name,
-// so key off both id and name to avoid recoloring legitimate rows.
+// into CHART_COLORS, which would collide with an earlier slice's color. Real
+// uncategorized spend also carries a null id, so key off the synthetic flag
+// rather than the id to avoid recoloring legitimate rows.
 function colorAt(item: SpendingChartItem, i: number): string {
-  if (item.id === null && item.name === "Other") return "var(--chart-neutral)";
+  if (item.synthetic) return "var(--chart-neutral)";
   return CHART_COLORS[i % CHART_COLORS.length];
 }
 
@@ -40,13 +42,15 @@ export function SpendingChart({ data, viewMode, onItemClick }: SpendingChartProp
   const otherTotal = data.slice(8).reduce((sum, d) => sum + d.value, 0);
   const chartData: SpendingChartItem[] =
     otherTotal > 0
-      ? [...top8, { id: null, name: "Other", value: otherTotal }]
+      ? [...top8, { id: null, name: "Other", value: otherTotal, synthetic: true }]
       : top8;
 
   function handleClick(index: number) {
     if (!onItemClick) return;
     const item = chartData[index];
-    if (item) onItemClick({ id: item.id, name: item.name });
+    // "Other" spans several categories, which drill-down can't express — a null
+    // id there would be read as uncategorized, so leave the slice inert.
+    if (item && !item.synthetic) onItemClick({ id: item.id, name: item.name });
   }
 
   if (viewMode === "donut") {
diff --git a/src/components/organisms/drill-down-sheet.tsx b/src/components/organisms/drill-down-sheet.tsx
index 435e7b4..82f45d7 100644
--- a/src/components/organisms/drill-down-sheet.tsx
+++ b/src/components/organisms/drill-down-sheet.tsx
@@ -13,11 +13,13 @@ import {
 import { Skeleton } from "@/components/ui/skeleton";
 import { TransactionListPanel } from "@/components/molecules/transaction-list-panel";
 import { getDrillDownTransactions } from "@/actions/reports";
+import { drillDownTransactionsUrl } from "@/lib/drill-down-url";
 import { centsToDisplay } from "@/lib/money";
 import type { TransactionRow } from "@/queries/transactions";
 
 export interface DrillDownFilter {
-  categoryId?: string;
+  /** A category id, `null` for uncategorized, `undefined` for no category filter. */
+  categoryId?: string | null;
   categoryName: string;
   month?: string;
   type?: "income" | "expense";
@@ -54,17 +56,21 @@ export function DrillDownSheet({ filter, dateFrom, dateTo, onClose }: DrillDownS
       setRows(result.rows);
       setHasMore(result.hasMore);
     });
-  // eslint-disable-next-line react-hooks/exhaustive-deps -- derived values (effectiveDateFrom/To) already capture filter changes
-  }, [filter?.categoryId, filter?.month, filter?.type, effectiveDateFrom, effectiveDateTo]);
+  // Depend on the filter object itself, not its fields: an uncategorized
+  // drill-down carries `categoryId: null` alongside undefined month/type, which
+  // is field-for-field identical to the closed (null filter) state, so a field
+  // dependency list would never fire and the sheet would open empty.
+  }, [filter, effectiveDateFrom, effectiveDateTo]);
 
   const totalAmount = rows.reduce((s, r) => s + r.normalizedAmount, 0);
 
   const txnPageUrl = filter
-    ? `/transactions?${new URLSearchParams({
-        ...(filter.categoryId ? { category: filter.categoryId } : {}),
-        from: filter.month ? `${filter.month}-01` : dateFrom,
-        to: filter.month ? `${filter.month}-31` : dateTo,
-      }).toString()}`
+    ? drillDownTransactionsUrl({
+        categoryId: filter.categoryId,
+        month: filter.month,
+        dateFrom,
+        dateTo,
+      })
     : "/transactions";
 
   return (
diff --git a/src/components/organisms/report-spending.tsx b/src/components/organisms/report-spending.tsx
index 6590736..2a667ff 100644
--- a/src/components/organisms/report-spending.tsx
+++ b/src/components/organisms/report-spending.tsx
@@ -48,8 +48,9 @@ export function ReportSpending({ data, comparisonLabel: compLabel }: ReportSpend
   ];
 
   function handleDrillDown(item: { id: string | null; name: string }) {
+    // Keep the null: it means "uncategorized", not "every category".
     setDrillDown({
-      categoryId: item.id ?? undefined,
+      categoryId: item.id,
       categoryName: item.name,
       tabContext: "Spending",
     });
diff --git a/src/lib/drill-down-url.test.ts b/src/lib/drill-down-url.test.ts
new file mode 100644
index 0000000..0a7602b
--- /dev/null
+++ b/src/lib/drill-down-url.test.ts
@@ -0,0 +1,28 @@
+import { describe, it, expect } from "vitest";
+import { drillDownTransactionsUrl } from "./drill-down-url";
+
+describe("drillDownTransactionsUrl", () => {
+  const range = { dateFrom: "2026-06-01", dateTo: "2026-08-31" };
+
+  it("passes a real category through as its id", () => {
+    const url = drillDownTransactionsUrl({ categoryId: "cat-groceries", ...range });
+    expect(url).toBe("/transactions?category=cat-groceries&from=2026-06-01&to=2026-08-31");
+  });
+
+  it("encodes a null category as the uncategorized sentinel", () => {
+    const url = drillDownTransactionsUrl({ categoryId: null, ...range });
+    expect(new URLSearchParams(url.split("?")[1]).get("category")).toBe("uncategorized");
+  });
+
+  it("omits the category param entirely when no category is filtered", () => {
+    const url = drillDownTransactionsUrl(range);
+    expect(url).toBe("/transactions?from=2026-06-01&to=2026-08-31");
+  });
+
+  it("narrows the range to the month when drilling into one", () => {
+    const url = drillDownTransactionsUrl({ categoryId: null, month: "2026-07", ...range });
+    const params = new URLSearchParams(url.split("?")[1]);
+    expect(params.get("from")).toBe("2026-07-01");
+    expect(params.get("to")).toBe("2026-07-31");
+  });
+});
diff --git a/src/lib/drill-down-url.ts b/src/lib/drill-down-url.ts
new file mode 100644
index 0000000..fe00a52
--- /dev/null
+++ b/src/lib/drill-down-url.ts
@@ -0,0 +1,27 @@
+/**
+ * Build the "View all in Transactions" link behind a report drill-down.
+ *
+ * `categoryId` follows the query-layer convention: a string is a real category,
+ * `null` means "no category assigned", and `undefined` means "don't filter by
+ * category at all". The transactions page has no null in a URL, so it encodes
+ * the uncategorized case as the sentinel `category=uncategorized` (see
+ * `parse-transaction-filters.ts`).
+ */
+export function drillDownTransactionsUrl(params: {
+  categoryId?: string | null;
+  month?: string;
+  dateFrom: string;
+  dateTo: string;
+}): string {
+  const { categoryId, month, dateFrom, dateTo } = params;
+
+  const search = new URLSearchParams({
+    ...(categoryId === undefined
+      ? {}
+      : { category: categoryId ?? "uncategorized" }),
+    from: month ? `${month}-01` : dateFrom,
+    to: month ? `${month}-31` : dateTo,
+  });
+
+  return `/transactions?${search.toString()}`;
+}