diff --git a/ApiCore-Backend/src/varroa/varroa.service.spec.ts b/ApiCore-Backend/src/varroa/varroa.service.spec.ts
index 9237cc3..20f0de0 100644
--- a/ApiCore-Backend/src/varroa/varroa.service.spec.ts
+++ b/ApiCore-Backend/src/varroa/varroa.service.spec.ts
@@ -100,4 +100,106 @@ describe('VarroaService', () => {
     expect(queryArg.where.colonyId).toBe('colony-1');
     expect(queryArg.orderBy.date).toBe('asc');
   });
+
+  describe('calculatedValue auto-computation', () => {
+    it('computes mites/day for a natural mite fall count on create', async () => {
+      prisma.varroaMeasurement.create.mockResolvedValue(measurement);
+
+      await service.create(
+        {
+          colonyId: 'colony-1',
+          date: '2026-01-01',
+          method: 'NATURAL_MITE_FALL',
+          miteCount: 45,
+          durationMinutes: 3 * 24 * 60,
+        },
+        'user-1',
+      );
+
+      const [[createArg]] = prisma.varroaMeasurement.create.mock.calls as [
+        [{ data: { calculatedValue?: number } }],
+      ];
+      expect(createArg.data.calculatedValue).toBe(15);
+    });
+
+    it('does not compute calculatedValue for a non-time-based method', async () => {
+      prisma.varroaMeasurement.create.mockResolvedValue(measurement);
+
+      await service.create(
+        {
+          colonyId: 'colony-1',
+          date: '2026-01-01',
+          method: 'POWDERED_SUGAR',
+          miteCount: 8,
+        },
+        'user-1',
+      );
+
+      const [[createArg]] = prisma.varroaMeasurement.create.mock.calls as [
+        [{ data: { calculatedValue?: number } }],
+      ];
+      expect(createArg.data.calculatedValue).toBeUndefined();
+    });
+
+    it('respects an explicitly provided calculatedValue instead of computing one', async () => {
+      prisma.varroaMeasurement.create.mockResolvedValue(measurement);
+
+      await service.create(
+        {
+          colonyId: 'colony-1',
+          date: '2026-01-01',
+          method: 'NATURAL_MITE_FALL',
+          miteCount: 45,
+          durationMinutes: 3 * 24 * 60,
+          calculatedValue: 99,
+        },
+        'user-1',
+      );
+
+      const [[createArg]] = prisma.varroaMeasurement.create.mock.calls as [
+        [{ data: { calculatedValue?: number } }],
+      ];
+      expect(createArg.data.calculatedValue).toBe(99);
+    });
+
+    it('backfills calculatedValue on update when it was never set', async () => {
+      prisma.varroaMeasurement.findUnique.mockResolvedValue({
+        ...measurement,
+        method: 'NATURAL_MITE_FALL',
+        miteCount: null,
+        durationMinutes: null,
+        calculatedValue: null,
+      });
+      prisma.varroaMeasurement.update.mockResolvedValue(measurement);
+
+      await service.update(
+        'varroa-1',
+        { miteCount: 20, durationMinutes: 24 * 60 },
+        'user-1',
+      );
+
+      const [[updateArg]] = prisma.varroaMeasurement.update.mock.calls as [
+        [{ data: { calculatedValue?: number } }],
+      ];
+      expect(updateArg.data.calculatedValue).toBe(20);
+    });
+
+    it('never overwrites an already-stored calculatedValue on an unrelated edit', async () => {
+      prisma.varroaMeasurement.findUnique.mockResolvedValue({
+        ...measurement,
+        method: 'NATURAL_MITE_FALL',
+        miteCount: 45,
+        durationMinutes: 3 * 24 * 60,
+        calculatedValue: 15,
+      });
+      prisma.varroaMeasurement.update.mockResolvedValue(measurement);
+
+      await service.update('varroa-1', { assessment: 'stabil' }, 'user-1');
+
+      const [[updateArg]] = prisma.varroaMeasurement.update.mock.calls as [
+        [{ data: { calculatedValue?: number } }],
+      ];
+      expect(updateArg.data.calculatedValue).toBeUndefined();
+    });
+  });
 });
diff --git a/ApiCore-Backend/src/varroa/varroa.service.ts b/ApiCore-Backend/src/varroa/varroa.service.ts
index 53e068c..76fdeca 100644
--- a/ApiCore-Backend/src/varroa/varroa.service.ts
+++ b/ApiCore-Backend/src/varroa/varroa.service.ts
@@ -6,6 +6,30 @@ import { VarroaMeasurement } from '../../generated/prisma';
 import { CreateVarroaMeasurementDto } from './dto/create-varroa-measurement.dto';
 import { UpdateVarroaMeasurementDto } from './dto/update-varroa-measurement.dto';
 
+const MINUTES_PER_DAY = 24 * 60;
+
+// Natural mite fall is counted on a sticky-board insert left in the hive
+// for some duration and is conventionally normalized to a daily rate
+// ("Milben/Tag") - both the VARROA_THRESHOLD automation config
+// (thresholdMitesPerDay) and the annual PDF report already assume
+// calculatedValue is in that unit. The other methods (Puderzucker,
+// Waschmethode, Drohnenbrutkontrolle) report a different, non-time-based
+// metric (mites per fixed bee sample); there is no single verified
+// formula for those here, so calculatedValue is left for the user to
+// enter manually for those methods instead of guessing one.
+function computeNaturalMiteFallPerDay(
+  miteCount: number | null | undefined,
+  durationMinutes: number | null | undefined,
+): number | undefined {
+  if (miteCount === null || miteCount === undefined) {
+    return undefined;
+  }
+  if (!durationMinutes || durationMinutes <= 0) {
+    return undefined;
+  }
+  return (miteCount / durationMinutes) * MINUTES_PER_DAY;
+}
+
 @Injectable()
 export class VarroaService {
   constructor(
@@ -41,8 +65,18 @@ export class VarroaService {
     dto: CreateVarroaMeasurementDto,
     actingUserId: string,
   ): Promise<VarroaMeasurement> {
+    const calculatedValue =
+      dto.calculatedValue ??
+      (dto.method === 'NATURAL_MITE_FALL'
+        ? computeNaturalMiteFallPerDay(dto.miteCount, dto.durationMinutes)
+        : undefined);
     const measurement = await this.prisma.varroaMeasurement.create({
-      data: { ...dto, date: new Date(dto.date), userId: actingUserId },
+      data: {
+        ...dto,
+        calculatedValue,
+        date: new Date(dto.date),
+        userId: actingUserId,
+      },
     });
     await this.auditLog.record({
       entityType: 'VarroaMeasurement',
@@ -61,9 +95,27 @@ export class VarroaService {
     actingUserId: string,
   ): Promise<VarroaMeasurement> {
     const before = await this.findById(id);
+    // Only auto-fill calculatedValue when nothing has set it yet - never
+    // overwrite a value the user (or a prior auto-fill) already stored,
+    // even if this edit only touches an unrelated field like notes.
+    const shouldAutoCompute =
+      dto.calculatedValue === undefined && before.calculatedValue === null;
+    const method = dto.method ?? before.method;
+    const calculatedValue =
+      dto.calculatedValue ??
+      (shouldAutoCompute && method === 'NATURAL_MITE_FALL'
+        ? computeNaturalMiteFallPerDay(
+            dto.miteCount ?? before.miteCount,
+            dto.durationMinutes ?? before.durationMinutes,
+          )
+        : undefined);
     const measurement = await this.prisma.varroaMeasurement.update({
       where: { id },
-      data: { ...dto, date: dto.date ? new Date(dto.date) : undefined },
+      data: {
+        ...dto,
+        calculatedValue,
+        date: dto.date ? new Date(dto.date) : undefined,
+      },
     });
     await this.auditLog.record({
       entityType: 'VarroaMeasurement',