diff --git a/api/v1beta1/spannerautoscaler_webhook.go b/api/v1beta1/spannerautoscaler_webhook.go
index 0cafd26..d816235 100644
--- a/api/v1beta1/spannerautoscaler_webhook.go
+++ b/api/v1beta1/spannerautoscaler_webhook.go
@@ -161,19 +161,9 @@ func (r *SpannerAutoscaler) validateAuthentication() *field.Error {
 	return nil
 }
 
-// exactlyOneOfBools returns true if exactly one of the given values is true.
-func exactlyOneOfBools(values ...bool) bool {
-	count := 0
-	for _, v := range values {
-		if v {
-			count++
-		}
-	}
-	return count == 1
-}
-
 func validateTargetCPUUtilization(cpu TargetCPUUtilization) *field.Error {
-	if !exactlyOneOfBools(cpu.HighPriority != nil, cpu.Total != nil) {
+	// XOR: exactly one of the two fields must be set.
+	if (cpu.HighPriority != nil) == (cpu.Total != nil) {
 		return field.Invalid(
 			field.NewPath("spec", "scaleConfig", "targetCPUUtilization"),
 			cpu,
diff --git a/internal/controller/spannerautoscaler_controller.go b/internal/controller/spannerautoscaler_controller.go
index 76a4f12..68b7572 100644
--- a/internal/controller/spannerautoscaler_controller.go
+++ b/internal/controller/spannerautoscaler_controller.go
@@ -756,12 +756,8 @@ func calcDesiredProcessingUnits(sa spannerv1beta1.SpannerAutoscaler) int {
 func calcDesiredPURange(sa spannerv1beta1.SpannerAutoscaler) (int, int, bool) {
 	changed := false
 	var desiredMin, desiredMax int
-	for i, sched := range sa.Status.CurrentlyActiveSchedules {
-		if i == 0 {
-			desiredMin = sched.AdditionalPU
-		} else if sched.AdditionalPU < desiredMin {
-			desiredMin = sched.AdditionalPU
-		}
+	for _, sched := range sa.Status.CurrentlyActiveSchedules {
+		desiredMin += sched.AdditionalPU
 		desiredMax += sched.AdditionalPU
 	}
 
diff --git a/internal/controller/spannerautoscaler_controller_test.go b/internal/controller/spannerautoscaler_controller_test.go
index ad4f20e..f221ed4 100644
--- a/internal/controller/spannerautoscaler_controller_test.go
+++ b/internal/controller/spannerautoscaler_controller_test.go
@@ -555,4 +555,83 @@ var _ = Describe("Get and overwrite interval", func() {
 	})
 })
 
+var _ = Describe("Calculate Desired PU Range", func() {
+	baseSpec := func(min, max int) spannerv1beta1.SpannerAutoscaler {
+		sa := spannerv1beta1.SpannerAutoscaler{}
+		sa.Spec.ScaleConfig.ProcessingUnits.Min = min
+		sa.Spec.ScaleConfig.ProcessingUnits.Max = max
+		return sa
+	}
+
+	It("returns spec min/max when no active schedules", func() {
+		sa := baseSpec(1000, 10000)
+		sa.Status.DesiredMinPUs = 1000
+		sa.Status.DesiredMaxPUs = 10000
+		gotMin, gotMax, changed := calcDesiredPURange(sa)
+		Expect(gotMin).To(Equal(1000))
+		Expect(gotMax).To(Equal(10000))
+		Expect(changed).To(BeFalse())
+	})
+
+	It("adds AdditionalPU to spec min/max for a single active schedule", func() {
+		sa := baseSpec(1000, 10000)
+		sa.Status.CurrentlyActiveSchedules = []spannerv1beta1.ActiveSchedule{
+			{AdditionalPU: 2000},
+		}
+		gotMin, gotMax, changed := calcDesiredPURange(sa)
+		Expect(gotMin).To(Equal(3000))
+		Expect(gotMax).To(Equal(12000))
+		Expect(changed).To(BeTrue())
+	})
+
+	It("sums AdditionalPU from all active schedules for both min and max", func() {
+		sa := baseSpec(1000, 10000)
+		sa.Status.CurrentlyActiveSchedules = []spannerv1beta1.ActiveSchedule{
+			{AdditionalPU: 1000},
+			{AdditionalPU: 5000},
+		}
+		gotMin, gotMax, changed := calcDesiredPURange(sa)
+		// desiredMin = 1000 + (1000 + 5000) = 7000
+		// desiredMax = 10000 + (1000 + 5000) = 16000
+		Expect(gotMin).To(Equal(7000))
+		Expect(gotMax).To(Equal(16000))
+		Expect(changed).To(BeTrue())
+	})
+
+	It("rounds up desiredMin and desiredMax to the next 1000 when above 1000 and not a multiple", func() {
+		sa := baseSpec(1000, 10000)
+		sa.Status.CurrentlyActiveSchedules = []spannerv1beta1.ActiveSchedule{
+			{AdditionalPU: 1500},
+		}
+		gotMin, gotMax, changed := calcDesiredPURange(sa)
+		// desiredMin = 1000 + 1500 = 2500 → rounded up to 3000
+		// desiredMax = 10000 + 1500 = 11500 → rounded up to 12000
+		Expect(gotMin).To(Equal(3000))
+		Expect(gotMax).To(Equal(12000))
+		Expect(changed).To(BeTrue())
+	})
+
+	It("does not round when desiredMin/Max is already a multiple of 1000", func() {
+		sa := baseSpec(1000, 10000)
+		sa.Status.CurrentlyActiveSchedules = []spannerv1beta1.ActiveSchedule{
+			{AdditionalPU: 3000},
+		}
+		gotMin, gotMax, changed := calcDesiredPURange(sa)
+		Expect(gotMin).To(Equal(4000))
+		Expect(gotMax).To(Equal(13000))
+		Expect(changed).To(BeTrue())
+	})
+
+	It("reports no change when computed values match current status", func() {
+		sa := baseSpec(1000, 10000)
+		sa.Status.CurrentlyActiveSchedules = []spannerv1beta1.ActiveSchedule{
+			{AdditionalPU: 2000},
+		}
+		sa.Status.DesiredMinPUs = 3000
+		sa.Status.DesiredMaxPUs = 12000
+		_, _, changed := calcDesiredPURange(sa)
+		Expect(changed).To(BeFalse())
+	})
+})
+
 func intPtr(i int) *int { return &i }