diff --git a/packages/api/src/__tests__/utilization-category-support.test.ts b/packages/api/src/__tests__/utilization-category-support.test.ts
new file mode 100644
index 0000000..bb31394
--- /dev/null
+++ b/packages/api/src/__tests__/utilization-category-support.test.ts
@@ -0,0 +1,73 @@
+import { TRPCError } from "@trpc/server";
+import { describe, expect, it, vi } from "vitest";
+import {
+  assertUtilizationCategoryCodeAvailable,
+  buildUtilizationCategoryCreateData,
+  buildUtilizationCategoryListWhere,
+  buildUtilizationCategoryUpdateData,
+  unsetDefaultUtilizationCategory,
+} from "../router/utilization-category-support.js";
+
+describe("utilization category support", () => {
+  it("builds list filters", () => {
+    expect(buildUtilizationCategoryListWhere({ isActive: true })).toEqual({
+      isActive: true,
+    });
+  });
+
+  it("rejects duplicate codes outside the ignored id", async () => {
+    const db = {
+      utilizationCategory: {
+        findUnique: vi.fn().mockResolvedValue({ id: "util_existing", code: "CHARGEABLE" }),
+      },
+    } as never;
+
+    await expect(assertUtilizationCategoryCodeAvailable(db, "CHARGEABLE")).rejects.toBeInstanceOf(TRPCError);
+  });
+
+  it("unsets the current default with and without an ignored id", async () => {
+    const db = {
+      utilizationCategory: {
+        updateMany: vi.fn().mockResolvedValue({ count: 1 }),
+      },
+    } as never;
+
+    await unsetDefaultUtilizationCategory(db);
+    await unsetDefaultUtilizationCategory(db, "util_keep");
+
+    expect(db.utilizationCategory.updateMany).toHaveBeenNthCalledWith(1, {
+      where: { isDefault: true },
+      data: { isDefault: false },
+    });
+    expect(db.utilizationCategory.updateMany).toHaveBeenNthCalledWith(2, {
+      where: { isDefault: true, id: { not: "util_keep" } },
+      data: { isDefault: false },
+    });
+  });
+
+  it("builds create and sparse update payloads", () => {
+    expect(buildUtilizationCategoryCreateData({
+      code: "CHARGEABLE",
+      name: "Chargeable",
+      description: "Revenue-generating project work",
+      sortOrder: 1,
+      isDefault: true,
+    })).toEqual({
+      code: "CHARGEABLE",
+      name: "Chargeable",
+      description: "Revenue-generating project work",
+      sortOrder: 1,
+      isDefault: true,
+    });
+
+    expect(buildUtilizationCategoryUpdateData({
+      description: null,
+      isActive: false,
+      isDefault: false,
+    })).toEqual({
+      description: null,
+      isActive: false,
+      isDefault: false,
+    });
+  });
+});
diff --git a/packages/api/src/router/utilization-category-support.ts b/packages/api/src/router/utilization-category-support.ts
new file mode 100644
index 0000000..32ddbf4
--- /dev/null
+++ b/packages/api/src/router/utilization-category-support.ts
@@ -0,0 +1,76 @@
+import type { Prisma, PrismaClient } from "@capakraken/db";
+import {
+  CreateUtilizationCategorySchema,
+  UpdateUtilizationCategorySchema,
+} from "@capakraken/shared";
+import { TRPCError } from "@trpc/server";
+import { z } from "zod";
+
+type UtilizationCategoryDb = Pick<PrismaClient, "utilizationCategory">;
+
+type UtilizationCategoryListInput = {
+  isActive?: boolean | undefined;
+};
+
+type CreateUtilizationCategoryInput = z.infer<typeof CreateUtilizationCategorySchema>;
+type UpdateUtilizationCategoryInput = z.infer<typeof UpdateUtilizationCategorySchema>;
+
+export function buildUtilizationCategoryListWhere(
+  input: UtilizationCategoryListInput,
+): Prisma.UtilizationCategoryWhereInput {
+  return {
+    ...(input.isActive !== undefined ? { isActive: input.isActive } : {}),
+  };
+}
+
+export async function assertUtilizationCategoryCodeAvailable(
+  db: UtilizationCategoryDb,
+  code: string,
+  ignoreId?: string,
+): Promise<void> {
+  const existing = await db.utilizationCategory.findUnique({ where: { code } });
+  if (existing && existing.id !== ignoreId) {
+    throw new TRPCError({
+      code: "CONFLICT",
+      message: `Code "${code}" already exists`,
+    });
+  }
+}
+
+export async function unsetDefaultUtilizationCategory(
+  db: UtilizationCategoryDb,
+  ignoreId?: string,
+): Promise<void> {
+  await db.utilizationCategory.updateMany({
+    where: {
+      isDefault: true,
+      ...(ignoreId ? { id: { not: ignoreId } } : {}),
+    },
+    data: { isDefault: false },
+  });
+}
+
+export function buildUtilizationCategoryCreateData(
+  input: CreateUtilizationCategoryInput,
+): Prisma.UtilizationCategoryUncheckedCreateInput {
+  return {
+    code: input.code,
+    name: input.name,
+    ...(input.description !== undefined ? { description: input.description } : {}),
+    sortOrder: input.sortOrder,
+    isDefault: input.isDefault,
+  };
+}
+
+export function buildUtilizationCategoryUpdateData(
+  input: UpdateUtilizationCategoryInput,
+): Prisma.UtilizationCategoryUncheckedUpdateInput {
+  return {
+    ...(input.code !== undefined ? { code: input.code } : {}),
+    ...(input.name !== undefined ? { name: input.name } : {}),
+    ...(input.description !== undefined ? { description: input.description } : {}),
+    ...(input.sortOrder !== undefined ? { sortOrder: input.sortOrder } : {}),
+    ...(input.isActive !== undefined ? { isActive: input.isActive } : {}),
+    ...(input.isDefault !== undefined ? { isDefault: input.isDefault } : {}),
+  };
+}
diff --git a/packages/api/src/router/utilization-category.ts b/packages/api/src/router/utilization-category.ts
index 60b40a0..97d469a 100644
--- a/packages/api/src/router/utilization-category.ts
+++ b/packages/api/src/router/utilization-category.ts
@@ -2,20 +2,24 @@ import {
   CreateUtilizationCategorySchema,
   UpdateUtilizationCategorySchema,
 } from "@capakraken/shared";
-import { TRPCError } from "@trpc/server";
 import { z } from "zod";
 import { findUniqueOrThrow } from "../db/helpers.js";
 import { createAuditEntry } from "../lib/audit.js";
 import { adminProcedure, createTRPCRouter, planningReadProcedure } from "../trpc.js";
+import {
+  assertUtilizationCategoryCodeAvailable,
+  buildUtilizationCategoryCreateData,
+  buildUtilizationCategoryListWhere,
+  buildUtilizationCategoryUpdateData,
+  unsetDefaultUtilizationCategory,
+} from "./utilization-category-support.js";
 
 export const utilizationCategoryRouter = createTRPCRouter({
   list: planningReadProcedure
     .input(z.object({ isActive: z.boolean().optional() }).optional())
     .query(async ({ ctx, input }) => {
       return ctx.db.utilizationCategory.findMany({
-        where: {
-          ...(input?.isActive !== undefined ? { isActive: input.isActive } : {}),
-        },
+        where: buildUtilizationCategoryListWhere(input ?? {}),
         orderBy: { sortOrder: "asc" },
       });
     }),
@@ -36,27 +40,15 @@ export const utilizationCategoryRouter = createTRPCRouter({
   create: adminProcedure
     .input(CreateUtilizationCategorySchema)
     .mutation(async ({ ctx, input }) => {
-      const existing = await ctx.db.utilizationCategory.findUnique({ where: { code: input.code } });
-      if (existing) {
-        throw new TRPCError({ code: "CONFLICT", message: `Code "${input.code}" already exists` });
-      }
+      await assertUtilizationCategoryCodeAvailable(ctx.db, input.code);
 
       // If setting as default, unset the current default first
       if (input.isDefault) {
-        await ctx.db.utilizationCategory.updateMany({
-          where: { isDefault: true },
-          data: { isDefault: false },
-        });
+        await unsetDefaultUtilizationCategory(ctx.db);
       }
 
       const created = await ctx.db.utilizationCategory.create({
-        data: {
-          code: input.code,
-          name: input.name,
-          ...(input.description !== undefined ? { description: input.description } : {}),
-          sortOrder: input.sortOrder,
-          isDefault: input.isDefault,
-        },
+        data: buildUtilizationCategoryCreateData(input),
       });
 
       void createAuditEntry({
@@ -82,32 +74,19 @@ export const utilizationCategoryRouter = createTRPCRouter({
       );
 
       if (input.data.code && input.data.code !== existing.code) {
-        const conflict = await ctx.db.utilizationCategory.findUnique({ where: { code: input.data.code } });
-        if (conflict) {
-          throw new TRPCError({ code: "CONFLICT", message: `Code "${input.data.code}" already exists` });
-        }
+        await assertUtilizationCategoryCodeAvailable(ctx.db, input.data.code, existing.id);
       }
 
       // If setting as default, unset others
       if (input.data.isDefault) {
-        await ctx.db.utilizationCategory.updateMany({
-          where: { isDefault: true, id: { not: input.id } },
-          data: { isDefault: false },
-        });
+        await unsetDefaultUtilizationCategory(ctx.db, input.id);
       }
 
       const before = existing as unknown as Record<string, unknown>;
 
       const updated = await ctx.db.utilizationCategory.update({
         where: { id: input.id },
-        data: {
-          ...(input.data.code !== undefined ? { code: input.data.code } : {}),
-          ...(input.data.name !== undefined ? { name: input.data.name } : {}),
-          ...(input.data.description !== undefined ? { description: input.data.description } : {}),
-          ...(input.data.sortOrder !== undefined ? { sortOrder: input.data.sortOrder } : {}),
-          ...(input.data.isActive !== undefined ? { isActive: input.data.isActive } : {}),
-          ...(input.data.isDefault !== undefined ? { isDefault: input.data.isDefault } : {}),
-        },
+        data: buildUtilizationCategoryUpdateData(input.data),
       });
 
       void createAuditEntry({