diff --git a/internal/controllers/admins.go b/internal/controllers/admins.go
index 50c6e59..0e63510 100644
--- a/internal/controllers/admins.go
+++ b/internal/controllers/admins.go
@@ -24,6 +24,7 @@ func (s Server) GetAllActiveSubscriptions(ctx echo.Context) error {
 		Preload("Quotas.ResourceType").
 		Preload("Usages").
 		Preload("Usages.ResourceType").
+		Preload("PlanRate").
 		Where(
 			s.GORMDB.WithContext(context).
 				Where("CURRENT_TIMESTAMP BETWEEN subscriptions.effective_start_date AND subscriptions.effective_end_date").
diff --git a/internal/db/subscriptions.go b/internal/db/subscriptions.go
index cd4d379..fc7d6f8 100644
--- a/internal/db/subscriptions.go
+++ b/internal/db/subscriptions.go
@@ -12,20 +12,29 @@ import (
 	"gorm.io/gorm/clause"
 )
 
-// QuotasFromPlan generates a set of quotas from the plan quota defaults in a plan. This function assumes that the
-// given plan already contains the plan quota defaults.
+// QuotasFromPlan generates a set of quotas from the plan quota defaults in a plan.
 func QuotasFromPlan(plan *model.Plan, periods int32) []model.Quota {
-	result := make([]model.Quota, len(plan.PlanQuotaDefaults))
-	for i, quotaDefault := range plan.PlanQuotaDefaults {
+
+	// Get the active plan quota defaults from the plan.
+	pqds := plan.GetDefaultQuotaValues()
+
+	// Build the array of quotas.
+	result := make([]model.Quota, len(pqds))
+
+	// Populate the quotas.
+	currentIndex := 0
+	for _, quotaDefault := range pqds {
 		quotaValue := quotaDefault.QuotaValue
 		if quotaDefault.ResourceType.Consumable {
 			quotaValue *= float64(periods)
 		}
-		result[i] = model.Quota{
+		result[currentIndex] = model.Quota{
 			Quota:          quotaValue,
 			ResourceTypeID: quotaDefault.ResourceTypeID,
 		}
+		currentIndex++
 	}
+
 	return result
 }
 
@@ -36,6 +45,12 @@ func SubscribeUserToPlan(
 	wrapMsg := "unable to add user plan"
 	var err error
 
+	// Look up the active plan rate.
+	planRate, err := plan.GetActivePlanRate()
+	if err != nil {
+		return nil, errors.Wrap(err, wrapMsg)
+	}
+
 	// Define the user plan.
 	effectiveStartDate := time.Now()
 	effectiveEndDate := opts.GetEndDate(effectiveStartDate)
@@ -46,6 +61,7 @@ func SubscribeUserToPlan(
 		PlanID:             plan.ID,
 		Quotas:             QuotasFromPlan(plan, opts.GetPeriods()),
 		Paid:               opts.IsPaid(),
+		PlanRateID:         planRate.ID,
 	}
 	err = db.WithContext(ctx).Create(&subscription).Error
 	if err != nil {
@@ -148,6 +164,7 @@ func GetSubscriptionDetails(ctx context.Context, db *gorm.DB, subscriptionID str
 		Preload("Quotas.ResourceType").
 		Preload("Usages").
 		Preload("Usages.ResourceType").
+		Preload("PlanRate").
 		Where("id = ?", subscriptionID).
 		First(&subscription).
 		Error
@@ -201,6 +218,7 @@ func ListSubscriptions(ctx context.Context, db *gorm.DB, params *SubscriptionLis
 		Preload("Quotas.ResourceType").
 		Preload("Usages").
 		Preload("Usages.ResourceType").
+		Preload("PlanRate").
 		Where(
 			db.Where("CURRENT_TIMESTAMP BETWEEN subscriptions.effective_start_date AND subscriptions.effective_end_date").
 				Or("CURRENT_TIMESTAMP > subscriptions.effective_start_date AND subscriptions.effective_end_date IS NULL"),
diff --git a/internal/model/plan.go b/internal/model/plan.go
index aafcb11..a23d69a 100644
--- a/internal/model/plan.go
+++ b/internal/model/plan.go
@@ -1,6 +1,7 @@
 package model
 
 import (
+	"fmt"
 	"time"
 )
 
@@ -28,30 +29,65 @@ type Plan struct {
 	PlanRates []PlanRate `json:"plan_rates,omitempty"`
 }
 
-// GetCurrentRate returns the current rate associated with the plan.
-func (p *Plan) GetCurrentRate() float64 {
-	var rate float64
-	currentDate := time.Now()
-	for _, planRate := range p.PlanRates {
-		if !planRate.EffectiveDate.After(currentDate) {
-			rate = planRate.Rate
+// Returns the currently active rate for a subscription plan. The active plan rate is the plan with the most recent
+// effective timestamp that occurs at or befor the curren time. This function assumes that the plan quota defaults are
+// sorted in ascending order by effective date.
+func (p *Plan) GetActivePlanRate() (*PlanRate, error) {
+	currentTime := time.Now()
+
+	// Find the active plan rate.
+	var activePlanRate *PlanRate
+	for _, pr := range p.PlanRates {
+		if pr.EffectiveDate.After(currentTime) {
+			break
 		}
+		activePlanRate = &pr
 	}
-	return rate
+
+	// It's an error for a plan not to have an active rate.
+	if activePlanRate == nil {
+		return nil, fmt.Errorf("no active rate found for subscription plan %s", *p.ID)
+	}
+
+	return activePlanRate, nil
 }
 
-// GetDefaultQuotaValue returns the default quota value associated with the resource type with the given name.
+// GetDefaultQuotaValue returns the default quota value associated with the resource type with the given name. This
+// funciton assumes that the plan quota defaults ar sorted in ascending order by effective date.
 func (p *Plan) GetDefaultQuotaValue(resourcetypeName string) float64 {
+	currentTime := time.Now()
+
+	// Find the active plan quota default value for the given resource type.
 	var value float64
 	for _, quotaDefault := range p.PlanQuotaDefaults {
+		if quotaDefault.EffectiveDate.After(currentTime) {
+			break
+		}
 		if quotaDefault.ResourceType.Name == resourcetypeName {
 			value = quotaDefault.QuotaValue
-			break
 		}
 	}
+
 	return value
 }
 
+// GetActiveQuotaValues returns the active quota values for a plan. This function assumes that the plan quota defaults
+// are sorted in ascending order by effective date.
+func (p *Plan) GetDefaultQuotaValues() map[string]*PlanQuotaDefault {
+	currentTime := time.Now()
+
+	// Find the active plan quota defaults for each resource type.
+	result := make(map[string]*PlanQuotaDefault)
+	for _, planQuotaDefault := range p.PlanQuotaDefaults {
+		if planQuotaDefault.EffectiveDate.After(currentTime) {
+			break
+		}
+		result[planQuotaDefault.ResourceType.Name] = &planQuotaDefault
+	}
+
+	return result
+}
+
 // PlanQuotaDefault define the structure for an Api Plan and Quota.
 type PlanQuotaDefault struct {
 	// The plan quota default identifier
@@ -135,6 +171,12 @@ type Subscription struct {
 
 	// True if the user paid for the subscription.
 	Paid bool `json:"paid"`
+
+	// The ID of the plan rate at the time the subscription was created.
+	PlanRateID *string `gorm:"type:uuid;not null" json:"-"`
+
+	// The plan rate at the time the subscription was created.
+	PlanRate *PlanRate `json:"plan_rate,omitempty"`
 }
 
 // GetCurrentUsageValue returns the current usage value for the resource type with the given resource type ID. Be