diff --git a/CHANGELOG.fr.md b/CHANGELOG.fr.md
index efd6279..23b0d31 100644
--- a/CHANGELOG.fr.md
+++ b/CHANGELOG.fr.md
@@ -2,6 +2,10 @@
 
 ## [Non publié]
 
+### Ajouté
+
+- Migration des catégories : les catégories personnalisées sans correspondance standard peuvent désormais être **fusionnées** dans une catégorie standard, au lieu d'être seulement mises de côté. Chaque catégorie personnalisée du bloc « Catégories personnalisées » reçoit le même sélecteur de cible que les lignes du seed — choisissez une feuille standard et ses transactions, budgets, mots-clés et fournisseurs y sont réassignés, puis la catégorie personnalisée est retirée. Laisser une catégorie personnalisée non mappée conserve le comportement précédent (regroupée sous « Catégories personnalisées (migration) ») et ne bloque jamais la migration (#259).
+
 ## [0.14.0] - 2026-07-18
 
 ### Modifié
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 0329f24..aab49ba 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,10 @@
 
 ## [Unreleased]
 
+### Added
+
+- Category migration: custom categories that have no standard match can now be **merged** into a standard category instead of only being set aside. Each custom category in the "Custom categories" block gets the same target picker as the seeded rows — choose a standard leaf and its transactions, budgets, keywords and suppliers are reassigned to it, then the custom category is removed. Leaving a custom category unmapped keeps the previous behaviour (grouped under "Custom categories (migration)") and never blocks the migration (#259).
+
 ## [0.14.0] - 2026-07-18
 
 ### Changed
diff --git a/src/components/categories-migration/StepSimulate.tsx b/src/components/categories-migration/StepSimulate.tsx
index e86c8d4..267f3a6 100644
--- a/src/components/categories-migration/StepSimulate.tsx
+++ b/src/components/categories-migration/StepSimulate.tsx
@@ -199,18 +199,20 @@ export default function StepSimulate({
               </p>
             </div>
           </div>
-          <ul className="text-sm space-y-1">
+          <ul className="space-y-1">
             {plan.preserved.map((row) => (
-              <li
-                key={row.v2CategoryId}
-                className="px-3 py-1.5 rounded-md bg-[var(--muted)] text-[var(--foreground)]"
-              >
-                <span className="font-medium">{row.v2CategoryName}</span>
-                <span className="text-xs text-[var(--muted-foreground)] ml-2">
-                  {t("categoriesSeed.migration.simulate.preserved.txCount", {
-                    count: transactionCountByV2Id.get(row.v2CategoryId) ?? 0,
-                  })}
-                </span>
+              <li key={row.v2CategoryId}>
+                <MappingRow
+                  row={row}
+                  isSelected={selectedRowV2Id === row.v2CategoryId}
+                  onSelect={onSelectRow}
+                  onResolve={onResolveRow}
+                  transactionCount={
+                    transactionCountByV2Id.get(row.v2CategoryId) ?? 0
+                  }
+                  targetCategories={targetCategories}
+                  resolveTarget={resolveTarget}
+                />
               </li>
             ))}
           </ul>
diff --git a/src/hooks/useCategoryMigration.test.ts b/src/hooks/useCategoryMigration.test.ts
index 6129d6e..3849af8 100644
--- a/src/hooks/useCategoryMigration.test.ts
+++ b/src/hooks/useCategoryMigration.test.ts
@@ -95,6 +95,46 @@ describe("migrationReducer", () => {
     expect(resolved.confidence).toBe("medium");
   });
 
+  it("RESOLVE_ROW resolves a preserved custom category and bumps its confidence (#259)", () => {
+    const plan = makePlan([makeRow(10, 1011)], [makeRow(9001, null)]);
+    const s1 = migrationReducer(INITIAL_STATE, { type: "LOAD_PLAN", plan });
+    const s2 = migrationReducer(s1, {
+      type: "RESOLVE_ROW",
+      v2CategoryId: 9001,
+      v1TargetId: 1111,
+      v1TargetName: "Épicerie régulière",
+    });
+    const merged = s2.plan!.preserved.find((r) => r.v2CategoryId === 9001)!;
+    expect(merged.v1TargetId).toBe(1111);
+    expect(merged.v1TargetName).toBe("Épicerie régulière");
+    expect(merged.confidence).toBe("medium");
+  });
+
+  it("RESOLVE_ROW on a preserved custom does NOT change unresolved (seed rows only) (#259)", () => {
+    // One unresolved seed row + one custom: the guard counts the seed only.
+    const plan = makePlan([makeRow(10, null)], [makeRow(9001, null)]);
+    const s1 = migrationReducer(INITIAL_STATE, { type: "LOAD_PLAN", plan });
+    expect(s1.unresolved).toBe(1);
+    const s2 = migrationReducer(s1, {
+      type: "RESOLVE_ROW",
+      v2CategoryId: 9001,
+      v1TargetId: 1111,
+      v1TargetName: "Épicerie régulière",
+    });
+    // Merging the custom must not decrement the seed-row guard.
+    expect(s2.unresolved).toBe(1);
+  });
+
+  it("GO_NEXT advances simulate -> consent with an unmerged custom still present (#259)", () => {
+    // All seed rows resolved, one custom left unmerged: the wizard must proceed.
+    const plan = makePlan([makeRow(10, 1011)], [makeRow(9001, null)]);
+    let s = migrationReducer(INITIAL_STATE, { type: "LOAD_PLAN", plan });
+    s = migrationReducer(s, { type: "GO_NEXT" }); // discover -> simulate
+    expect(s.step).toBe("simulate");
+    s = migrationReducer(s, { type: "GO_NEXT" }); // simulate -> consent
+    expect(s.step).toBe("consent");
+  });
+
   it("GO_NEXT blocks simulate -> consent when unresolved > 0", () => {
     const plan = makePlan([makeRow(10, null)]);
     let s = migrationReducer(INITIAL_STATE, { type: "LOAD_PLAN", plan });
diff --git a/src/hooks/useCategoryMigration.ts b/src/hooks/useCategoryMigration.ts
index 5c9dc52..ac25072 100644
--- a/src/hooks/useCategoryMigration.ts
+++ b/src/hooks/useCategoryMigration.ts
@@ -118,28 +118,36 @@ export function migrationReducer(
 
     case "RESOLVE_ROW": {
       if (state.plan === null) return state;
-      const rows = state.plan.rows.map((r) =>
+      // A resolved target can land on a seeded row (plan.rows) OR a custom
+      // category (plan.preserved) — the latter is the "merge a custom into a
+      // standard leaf" path (#259). Apply the target in whichever bucket holds
+      // the row; it is a no-op for the other one.
+      const applyTarget = (r: MappingRow): MappingRow =>
         r.v2CategoryId === action.v2CategoryId
           ? {
               ...r,
               v1TargetId: action.v1TargetId,
               v1TargetName: action.v1TargetName,
-              // Once a user resolves a row manually, bump the confidence badge
-              // to "medium" so the simulate table reflects their decision.
-              // We keep the reason as-is so that the tooltip still explains
-              // what the algorithm thought.
+              // Resolving a row manually bumps the confidence badge to "medium"
+              // so the table reflects the decision. Reason is left as-is so the
+              // tooltip still explains what the algorithm thought.
               confidence: r.confidence === "none" ? "medium" : r.confidence,
             }
-          : r,
-      );
+          : r;
+      const rows = state.plan.rows.map(applyTarget);
+      const preserved = state.plan.preserved.map(applyTarget);
       const plan: MigrationPlan = {
         ...state.plan,
         rows,
+        preserved,
         unresolved: rows.filter((r) => r.v1TargetId === null),
       };
       return {
         ...state,
         plan,
+        // `unresolved` gates the Next button and counts seeded rows ONLY. A
+        // custom left unmerged is a legitimate choice and must never block the
+        // wizard.
         unresolved: countUnresolved(rows),
       };
     }
diff --git a/src/i18n/locales/en.json b/src/i18n/locales/en.json
index 0dc580a..cc5cc61 100644
--- a/src/i18n/locales/en.json
+++ b/src/i18n/locales/en.json
@@ -1483,11 +1483,9 @@
           "total": "Total"
         },
         "preserved": {
-          "title_one": "{{count}} custom category preserved",
-          "title_other": "{{count}} custom categories preserved",
-          "body": "Your custom categories will be grouped under the parent \"Custom categories (migration)\". You can move or rename them at your own pace after the migration.",
-          "txCount_one": "{{count}} transaction",
-          "txCount_other": "{{count}} transactions"
+          "title_one": "{{count}} custom category",
+          "title_other": "{{count}} custom categories",
+          "body": "These categories have no standard equivalent. Pick a target to merge a category: its transactions, budgets, keywords and suppliers are reassigned to it and the category disappears. Leave the field empty to keep it as-is under \"Custom categories (migration)\"."
         },
         "panel": {
           "title": "Affected transactions",
diff --git a/src/i18n/locales/fr.json b/src/i18n/locales/fr.json
index 2fa5417..fb7aa62 100644
--- a/src/i18n/locales/fr.json
+++ b/src/i18n/locales/fr.json
@@ -1483,11 +1483,9 @@
           "total": "Total"
         },
         "preserved": {
-          "title_one": "{{count}} catégorie personnalisée préservée",
-          "title_other": "{{count}} catégories personnalisées préservées",
-          "body": "Vos catégories personnalisées seront regroupées sous le parent « Catégories personnalisées (migration) ». Vous pourrez les déplacer ou les renommer à votre rythme après la migration.",
-          "txCount_one": "{{count}} transaction",
-          "txCount_other": "{{count}} transactions"
+          "title_one": "{{count}} catégorie personnalisée",
+          "title_other": "{{count}} catégories personnalisées",
+          "body": "Ces catégories n'ont pas d'équivalent standard. Choisissez une cible pour fusionner une catégorie : ses transactions, budgets, mots-clés et fournisseurs y sont réassignés et la catégorie disparaît. Laissez le champ vide pour la conserver telle quelle sous « Catégories personnalisées (migration) »."
         },
         "panel": {
           "title": "Transactions impactées",
diff --git a/src/services/categoryMigrationService.test.ts b/src/services/categoryMigrationService.test.ts
index 9e20d58..f398bc5 100644
--- a/src/services/categoryMigrationService.test.ts
+++ b/src/services/categoryMigrationService.test.ts
@@ -303,6 +303,119 @@ describe("applyMigration — preserved custom categories", () => {
   });
 });
 
+// ---------------------------------------------------------------------------
+// Merged custom categories (#259)
+// ---------------------------------------------------------------------------
+
+describe("applyMigration — merged custom categories (#259)", () => {
+  it("reassigns transactions/budgets/keywords/suppliers of a merged custom to the chosen leaf", async () => {
+    // Custom category 9001 merged into leaf 1444.
+    await applyMigration(
+      makePlan([makeRow(22, 1111)], [makeRow(9001, 1444)]),
+      FAKE_BACKUP,
+    );
+    const merged = (re: RegExp) =>
+      fake.calls.filter(
+        (c) => re.test(c.sql) && (c.params?.[1] as number) === 9001,
+      );
+    // Each reassignment must target the chosen leaf (1444), keyed by the custom
+    // id (9001) — not merely be emitted.
+    expect(merged(/UPDATE transactions SET category_id/i)[0]?.params).toEqual([
+      1444, 9001,
+    ]);
+    expect(merged(/UPDATE budget_entries SET category_id/i)[0]?.params).toEqual([
+      1444, 9001,
+    ]);
+    expect(merged(/UPDATE keywords SET category_id/i)[0]?.params).toEqual([
+      1444, 9001,
+    ]);
+    expect(merged(/UPDATE suppliers SET category_id/i)[0]?.params).toEqual([
+      1444, 9001,
+    ]);
+  });
+
+  it("soft-deletes a merged custom (is_active=0) and does NOT re-parent it", async () => {
+    await applyMigration(
+      makePlan([makeRow(22, 1111)], [makeRow(9001, 1444)]),
+      FAKE_BACKUP,
+    );
+    const deactivate = fake.calls.filter(
+      (c) =>
+        /UPDATE categories SET is_active = 0 WHERE id = \$1/i.test(c.sql) &&
+        (c.params?.[0] as number) === 9001,
+    );
+    const reparent = fake.calls.filter(
+      (c) =>
+        /UPDATE categories SET parent_id = \$1 WHERE id = \$2/i.test(c.sql) &&
+        (c.params?.[1] as number) === 9001,
+    );
+    expect(deactivate.length).toBe(1);
+    expect(reparent.length).toBe(0);
+  });
+
+  it("does NOT create the custom parent when every preserved custom is merged", async () => {
+    await applyMigration(
+      makePlan([makeRow(22, 1111)], [makeRow(9001, 1444), makeRow(9002, 1555)]),
+      FAKE_BACKUP,
+    );
+    const parentInserts = fake.calls.filter(
+      (c) =>
+        /INSERT OR IGNORE INTO categories/i.test(c.sql) &&
+        (c.params?.[0] as number) === 2000,
+    );
+    expect(parentInserts.length).toBe(0);
+  });
+
+  it("creates the custom parent when at least one preserved custom is left unmerged", async () => {
+    await applyMigration(
+      makePlan([makeRow(22, 1111)], [makeRow(9001, 1444), makeRow(9002, null)]),
+      FAKE_BACKUP,
+    );
+    const parentInserts = fake.calls.filter(
+      (c) =>
+        /INSERT OR IGNORE INTO categories/i.test(c.sql) &&
+        (c.params?.[0] as number) === 2000,
+    );
+    expect(parentInserts.length).toBe(1);
+    // Only the unmerged custom (9002) is re-parented; the merged one (9001) is not.
+    const reparent = fake.calls.filter((c) =>
+      /UPDATE categories SET parent_id = \$1 WHERE id = \$2/i.test(c.sql),
+    );
+    expect(reparent.map((c) => c.params?.[1])).toEqual([9002]);
+  });
+
+  it("leaves no orphan when a custom PARENT is merged but its custom CHILD is not (regression)", async () => {
+    // plan.preserved is a flat list: a merged parent (9001 → 1444) and its
+    // unresolved child (9002). The child must land under the bucket (2000) and
+    // the parent be deactivated — the child never dangles under a dead parent.
+    await applyMigration(
+      makePlan([makeRow(22, 1111)], [makeRow(9001, 1444), makeRow(9002, null)]),
+      FAKE_BACKUP,
+    );
+    // Child re-parented under 2000.
+    const childReparent = fake.calls.filter(
+      (c) =>
+        /UPDATE categories SET parent_id = \$1 WHERE id = \$2/i.test(c.sql) &&
+        (c.params?.[1] as number) === 9002,
+    );
+    expect(childReparent.length).toBe(1);
+    expect(childReparent[0].params?.[0]).toBe(2000);
+    // Parent merged → deactivated, not re-parented.
+    const parentDeactivate = fake.calls.filter(
+      (c) =>
+        /UPDATE categories SET is_active = 0 WHERE id = \$1/i.test(c.sql) &&
+        (c.params?.[0] as number) === 9001,
+    );
+    const parentReparent = fake.calls.filter(
+      (c) =>
+        /UPDATE categories SET parent_id = \$1 WHERE id = \$2/i.test(c.sql) &&
+        (c.params?.[1] as number) === 9001,
+    );
+    expect(parentDeactivate.length).toBe(1);
+    expect(parentReparent.length).toBe(0);
+  });
+});
+
 // ---------------------------------------------------------------------------
 // Rollback on SQL failure
 // ---------------------------------------------------------------------------
diff --git a/src/services/categoryMigrationService.ts b/src/services/categoryMigrationService.ts
index 49e51f6..66be851 100644
--- a/src/services/categoryMigrationService.ts
+++ b/src/services/categoryMigrationService.ts
@@ -142,12 +142,17 @@ function validateBackup(backup: BackupResult): void {
   }
 }
 
-/** Build the v2Id → v1Id map from plan.rows (only resolved targets are kept). */
+/** True when a mapping row carries a concrete v1 target (resolved / merged). */
+function isResolvedTarget(row: MappingRow): boolean {
+  return row.v1TargetId !== null && row.v1TargetId !== undefined;
+}
+
+/** Build the v2Id → v1Id map from mapping rows (only resolved targets kept). */
 function buildMappingFromRows(rows: MappingRow[]): Map<number, number> {
   const map = new Map<number, number>();
   for (const row of rows) {
-    if (row.v1TargetId !== null && row.v1TargetId !== undefined) {
-      map.set(row.v2CategoryId, row.v1TargetId);
+    if (isResolvedTarget(row)) {
+      map.set(row.v2CategoryId, row.v1TargetId as number);
     }
   }
   return map;
@@ -190,13 +195,21 @@ async function applyMigrationInTransaction(
   backup: BackupResult,
   outcome: MigrationOutcome,
 ): Promise<MigrationOutcome> {
-  const mapping = buildMappingFromRows(plan.rows);
+  // Seeded rows AND merged custom categories (preserved rows the user gave a
+  // target) share the same rewrite: their transactions, budgets, keywords and
+  // suppliers are reassigned to the chosen v1 leaf. Unresolved preserved rows
+  // have a null target and are filtered out by buildMappingFromRows.
+  const allMappableRows = [...plan.rows, ...plan.preserved];
+  const mapping = buildMappingFromRows(allMappableRows);
 
   await db.execute("BEGIN");
   try {
-    // 1. Optionally create the "custom categories (migration)" parent.
+    // 1. Optionally create the "custom categories (migration)" parent — only
+    //    when at least one custom category is left UNMERGED. If every custom
+    //    was merged into a standard leaf, the bucket would be empty, so skip it.
     let customParentId: number | null = null;
-    if (plan.preserved.length > 0) {
+    const hasUnmergedPreserved = plan.preserved.some((p) => !isResolvedTarget(p));
+    if (hasUnmergedPreserved) {
       // Use INSERT OR IGNORE so a re-run never throws on the PK.
       await db.execute(
         `INSERT OR IGNORE INTO categories
@@ -322,6 +335,9 @@ async function applyMigrationInTransaction(
     //    at a v2 structural parent in the 1..6 range): children follow naturally.
     if (customParentId !== null) {
       for (const preservedRow of plan.preserved) {
+        // Merged customs are deactivated in the soft-delete step below, not
+        // re-parented — only the ones left unmerged move under the bucket.
+        if (isResolvedTarget(preservedRow)) continue;
         const r = await db.execute(
           `UPDATE categories SET parent_id = $1 WHERE id = $2`,
           [customParentId, preservedRow.v2CategoryId],
@@ -330,18 +346,16 @@ async function applyMigrationInTransaction(
       }
     }
 
-    // 9. Soft-delete v2 seeded categories that are now unreferenced.
-    //    We deactivate instead of hard-deleting so that any historical
-    //    reference we might have missed stays intact (is_active=0 hides them
-    //    from the UI lists). We explicitly only target the v2 seed id range
-    //    (< 1000) AND ids that map in our plan — this avoids touching user
-    //    custom categories that may also have parent_id < 1000 structural.
-    for (const row of plan.rows) {
-      // Only deactivate rows that were part of the v2 seed AND we successfully
-      // mapped to a v1 target. Rows with no v1 target (unresolved review) are
-      // left alone — in the UX, the consent step is blocked until all rows
-      // are resolved, so this should be dead code, but it is a safety net.
-      if (row.v1TargetId === null) continue;
+    // 9. Soft-delete every category whose data we just rewrote: mapped v2 seed
+    //    rows AND merged custom categories. We deactivate (is_active=0) instead
+    //    of hard-deleting so any historical reference we might have missed stays
+    //    intact and hidden from the UI lists.
+    for (const row of allMappableRows) {
+      // Skip rows with no target. Seed rows can't reach here (consent is
+      // blocked until they're all resolved), but a custom left unmerged
+      // legitimately does — it must stay alive under the bucket, not be
+      // deactivated.
+      if (!isResolvedTarget(row)) continue;
       const r = await db.execute(
         `UPDATE categories SET is_active = 0 WHERE id = $1`,
         [row.v2CategoryId],