diff --git a/cmd/e2e/log_queries_test.go b/cmd/e2e/log_queries_test.go
index e6aaf266..62824fdd 100644
--- a/cmd/e2e/log_queries_test.go
+++ b/cmd/e2e/log_queries_test.go
@@ -80,7 +80,7 @@ func (s *basicSuite) TestLogQueries_Attempts() {
 		s.Equal(setup.destinationID, first["destination_id"])
 		s.NotEmpty(first["status"])
 		s.NotEmpty(first["time"])
-		s.Equal(float64(0), first["attempt_number"])
+		s.Equal(float64(1), first["attempt_number"])
 	})
 
 	s.Run("filter by destination_id", func() {
diff --git a/cmd/e2e/retry_test.go b/cmd/e2e/retry_test.go
index 98a85280..6b9b7ccb 100644
--- a/cmd/e2e/retry_test.go
+++ b/cmd/e2e/retry_test.go
@@ -34,8 +34,8 @@ func (s *basicSuite) TestRetry_FailedDeliveryAutoRetries() {
 	s.Require().GreaterOrEqual(len(resp.Models), 2)
 
 	for i, atm := range resp.Models {
-		s.Equal(float64(i), atm["attempt_number"],
-			"attempt %d should have attempt_number=%d (automated retry increments)", i, i)
+		s.Equal(float64(i+1), atm["attempt_number"],
+			"attempt %d should have attempt_number=%d (automated retry increments)", i, i+1)
 	}
 }
 
@@ -51,14 +51,14 @@ func (s *basicSuite) TestRetry_ManualRetryCreatesNewAttempt() {
 	// Wait for initial delivery
 	s.waitForNewAttempts(tenant.ID, 1)
 
-	// Verify first attempt has attempt_number=0
+	// Verify first attempt has attempt_number=1
 	var attResp struct {
 		Models []map[string]any `json:"models"`
 	}
 	status := s.doJSON(http.MethodGet, s.apiURL("/attempts?tenant_id="+tenant.ID+"&event_id="+eventID), nil, &attResp)
 	s.Require().Equal(http.StatusOK, status)
 	s.Require().NotEmpty(attResp.Models)
-	s.Equal(float64(0), attResp.Models[0]["attempt_number"])
+	s.Equal(float64(1), attResp.Models[0]["attempt_number"])
 
 	// Manual retry
 	retryStatus := s.retryEvent(eventID, dest.ID)
@@ -75,9 +75,9 @@ func (s *basicSuite) TestRetry_ManualRetryCreatesNewAttempt() {
 	s.Require().Equal(http.StatusOK, status)
 	s.Require().Len(verifyResp.Models, 2)
 
-	// Both should have attempt_number=0 (manual retry resets)
+	// Both should have attempt_number=1 (manual retry resets)
 	for _, atm := range verifyResp.Models {
-		s.Equal(float64(0), atm["attempt_number"])
+		s.Equal(float64(1), atm["attempt_number"])
 	}
 
 	// Verify one manual=true
diff --git a/internal/deliverymq/messagehandler.go b/internal/deliverymq/messagehandler.go
index f077c99d..2d94ec21 100644
--- a/internal/deliverymq/messagehandler.go
+++ b/internal/deliverymq/messagehandler.go
@@ -360,8 +360,8 @@ func (h *messageHandler) shouldScheduleRetry(task models.DeliveryTask, err error
 	if !errors.As(err, &pubErr) {
 		return false
 	}
-	// Attempt starts at 0 for initial attempt, so we can compare directly
-	return task.Attempt < h.retryMaxLimit
+	// Attempt starts at 1 for initial attempt, so use <= to allow retryMaxLimit total attempts
+	return task.Attempt <= h.retryMaxLimit
 }
 
 func (h *messageHandler) shouldNackError(err error) bool {
@@ -410,7 +410,11 @@ func (h *messageHandler) shouldNackDeliveryError(err error) bool {
 }
 
 func (h *messageHandler) scheduleRetry(ctx context.Context, task models.DeliveryTask) error {
-	backoffDuration := h.retryBackoff.Duration(task.Attempt)
+	// Backoff expects a 0-based index (0 for first retry, 1 for second, etc.).
+	// attempt_number changed from 0-based to 1-based without migrating in-flight
+	// tasks, so clamp to 0 to safely handle any leftover Attempt=0 tasks.
+	backoffIndex := max(task.Attempt-1, 0)
+	backoffDuration := h.retryBackoff.Duration(backoffIndex)
 
 	retryTask := RetryTaskFromDeliveryTask(task)
 	retryTaskStr, err := retryTask.ToString()
diff --git a/internal/models/tasks.go b/internal/models/tasks.go
index ed43187a..dd54d1cd 100644
--- a/internal/models/tasks.go
+++ b/internal/models/tasks.go
@@ -82,7 +82,7 @@ func NewDeliveryTask(event Event, destinationID string) DeliveryTask {
 	return DeliveryTask{
 		Event:         event,
 		DestinationID: destinationID,
-		Attempt:       0,
+		Attempt:       1,
 	}
 }