diff --git a/apps/api/src/characters/character-stats.service.spec.ts b/apps/api/src/characters/character-stats.service.spec.ts
new file mode 100644
index 0000000..45f8417
--- /dev/null
+++ b/apps/api/src/characters/character-stats.service.spec.ts
@@ -0,0 +1,115 @@
+// apps/api/src/characters/character-stats.service.spec.ts
+import { DataSource } from 'typeorm';
+import { CharacterStatsService } from './character-stats.service';
+import { Character } from './entities/character.entity';
+import { EquipmentSlot } from '../items/equipment-slot.enum';
+import { ItemDefinition } from '../items/entities/item-definition.entity';
+
+type EquippedFixture = {
+  slot: EquipmentSlot;
+  item: Partial<ItemDefinition>;
+};
+
+function fakeScope(equipped: EquippedFixture[]): Pick<DataSource, 'getRepository'> {
+  const rows = equipped.map((entry) => ({
+    slot: entry.slot,
+    characterItem: {
+      itemDefinition: {
+        weaponDamage: 0,
+        bonusHp: 0,
+        bonusAttack: 0,
+        bonusArmor: 0,
+        ...entry.item,
+      },
+    },
+  }));
+  return {
+    getRepository: () => ({ find: async () => rows }) as never,
+  } as unknown as Pick<DataSource, 'getRepository'>;
+}
+
+function character(overrides: Partial<Character> = {}): Character {
+  return {
+    id: 'character-1',
+    baseHp: 100,
+    baseAttack: 6,
+    currentHp: 90,
+    ...overrides,
+  } as Character;
+}
+
+describe('CharacterStatsService', () => {
+  const service = new CharacterStatsService({} as DataSource);
+
+  it('derives stats from the starting weapon alone', async () => {
+    const scope = fakeScope([{ slot: EquipmentSlot.WEAPON, item: { weaponDamage: 8 } }]);
+
+    const stats = await service.calculate(character(), scope);
+
+    expect(stats.attack).toBe(6);
+    expect(stats.weaponDamage).toBe(8);
+    expect(stats.maxHp).toBe(100);
+    expect(stats.armor).toBe(0);
+  });
+
+  it('applies Räuberklinge\'s weapon damage and bonus attack', async () => {
+    const scope = fakeScope([
+      { slot: EquipmentSlot.WEAPON, item: { weaponDamage: 11, bonusAttack: 1 } },
+    ]);
+
+    const stats = await service.calculate(character(), scope);
+
+    expect(stats.attack).toBe(7);
+    expect(stats.weaponDamage).toBe(11);
+  });
+
+  it('sums bonusArmor across multiple equipped armor pieces', async () => {
+    const scope = fakeScope([
+      { slot: EquipmentSlot.HEAD, item: { bonusArmor: 3 } },
+      { slot: EquipmentSlot.CHEST, item: { bonusArmor: 7 } },
+    ]);
+
+    const stats = await service.calculate(character(), scope);
+
+    expect(stats.armor).toBe(10);
+  });
+
+  it('sums bonusHp across equipped items on top of base HP', async () => {
+    const scope = fakeScope([
+      { slot: EquipmentSlot.HEAD, item: { bonusHp: 5 } },
+      { slot: EquipmentSlot.CHEST, item: { bonusHp: 10 } },
+    ]);
+
+    const stats = await service.calculate(character(), scope);
+
+    expect(stats.maxHp).toBe(115);
+  });
+
+  it('reports weaponDamage as 0 when no weapon is equipped', async () => {
+    const scope = fakeScope([{ slot: EquipmentSlot.HEAD, item: { bonusArmor: 3 } }]);
+
+    const stats = await service.calculate(character(), scope);
+
+    expect(stats.weaponDamage).toBe(0);
+  });
+
+  it('calculates Combat Power as HP/10 + attack*2 + weaponDamage*2 + armor*1.5', async () => {
+    const scope = fakeScope([
+      { slot: EquipmentSlot.WEAPON, item: { weaponDamage: 11, bonusAttack: 1 } },
+      { slot: EquipmentSlot.HEAD, item: { bonusArmor: 3, bonusHp: 5 } },
+    ]);
+
+    const stats = await service.calculate(character(), scope);
+
+    // maxHp=105, attack=7, weaponDamage=11, armor=3
+    expect(stats.combatPower).toBe(105 / 10 + 7 * 2 + 11 * 2 + 3 * 1.5);
+  });
+
+  it('passes currentHp through unchanged from the character', async () => {
+    const scope = fakeScope([]);
+
+    const stats = await service.calculate(character({ currentHp: 42 }), scope);
+
+    expect(stats.currentHp).toBe(42);
+  });
+});
diff --git a/apps/api/src/characters/character-stats.service.ts b/apps/api/src/characters/character-stats.service.ts
new file mode 100644
index 0000000..5d0e0a1
--- /dev/null
+++ b/apps/api/src/characters/character-stats.service.ts
@@ -0,0 +1,64 @@
+import { Injectable } from '@nestjs/common';
+import { DataSource } from 'typeorm';
+import { CharacterEquipment } from '../equipment/entities/character-equipment.entity';
+import { EquipmentSlot } from '../items/equipment-slot.enum';
+import { Character } from './entities/character.entity';
+
+export interface EffectiveCharacterStats {
+  maxHp: number;
+  currentHp: number;
+  attack: number;
+  weaponDamage: number;
+  armor: number;
+  combatPower: number;
+}
+
+type RepositoryScope = Pick<DataSource, 'getRepository'>;
+
+/**
+ * Single authoritative source of effective character stats (spec §18).
+ * Replaces the Slice 0.3 `CharacterCombatStatsService` shortcut.
+ */
+@Injectable()
+export class CharacterStatsService {
+  constructor(private readonly dataSource: DataSource) {}
+
+  async calculate(
+    character: Character,
+    scope?: RepositoryScope,
+  ): Promise<EffectiveCharacterStats> {
+    const db = scope ?? this.dataSource;
+    const equipped = await db.getRepository(CharacterEquipment).find({
+      where: { characterId: character.id },
+      relations: { characterItem: { itemDefinition: true } },
+    });
+
+    let weaponDamage = 0;
+    let bonusHp = 0;
+    let bonusAttack = 0;
+    let bonusArmor = 0;
+
+    for (const slot of equipped) {
+      const definition = slot.characterItem.itemDefinition;
+      if (slot.slot === EquipmentSlot.WEAPON) {
+        weaponDamage = definition.weaponDamage;
+      }
+      bonusHp += definition.bonusHp;
+      bonusAttack += definition.bonusAttack;
+      bonusArmor += definition.bonusArmor;
+    }
+
+    const maxHp = character.baseHp + bonusHp;
+    const attack = character.baseAttack + bonusAttack;
+    const armor = bonusArmor;
+
+    return {
+      maxHp,
+      currentHp: character.currentHp,
+      attack,
+      weaponDamage,
+      armor,
+      combatPower: maxHp / 10 + attack * 2 + weaponDamage * 2 + armor * 1.5,
+    };
+  }
+}