diff --git a/SeaHaven.DataServices/Helpers/WorkOrderBoardQueryFilters.cs b/SeaHaven.DataServices/Helpers/WorkOrderBoardQueryFilters.cs
index ba41941..f6d7bd6 100644
--- a/SeaHaven.DataServices/Helpers/WorkOrderBoardQueryFilters.cs
+++ b/SeaHaven.DataServices/Helpers/WorkOrderBoardQueryFilters.cs
@@ -71,8 +71,8 @@ namespace SeaHaven.DataServices.Helpers
             if (overdue && !hasTypes)
             {
                 return query.Where(w =>
-                    w.ScheduledDate != null
-                    && w.ScheduledDate.Value.Date < today
+                    w.DueDate != null
+                    && w.DueDate.Value.Date < today
                     && w.LifecycleStatus != LifecycleStatus.Completed
                     && w.LifecycleStatus != LifecycleStatus.Canceled);
             }
@@ -80,8 +80,8 @@ namespace SeaHaven.DataServices.Helpers
             if (overdue)
             {
                 return query.Where(w =>
-                    (w.ScheduledDate != null
-                     && w.ScheduledDate.Value.Date < today
+                    (w.DueDate != null
+                     && w.DueDate.Value.Date < today
                      && w.LifecycleStatus != LifecycleStatus.Completed
                      && w.LifecycleStatus != LifecycleStatus.Canceled)
                     || (w.WorkOrderType != null && typeFilters.Contains(w.WorkOrderType.Value)));
diff --git a/SeaHaven.DataServices/Helpers/WorkOrderBoardSearchFilter.cs b/SeaHaven.DataServices/Helpers/WorkOrderBoardSearchFilter.cs
index d6cf28d..3149f5c 100644
--- a/SeaHaven.DataServices/Helpers/WorkOrderBoardSearchFilter.cs
+++ b/SeaHaven.DataServices/Helpers/WorkOrderBoardSearchFilter.cs
@@ -60,8 +60,8 @@ namespace SeaHaven.DataServices.Helpers
                 || (w.WorkOrderType == WorkOrderType.AddOn && ("add-on".Contains(s) || "addon".Contains(s)))
                 || (w.WorkOrderType == WorkOrderType.Other && "other".Contains(s))
                 || ("overdue".Contains(s)
-                    && w.ScheduledDate != null
-                    && w.ScheduledDate.Value.Date < today
+                    && w.DueDate != null
+                    && w.DueDate.Value.Date < today
                     && w.LifecycleStatus != LifecycleStatus.Completed
                     && w.LifecycleStatus != LifecycleStatus.Canceled)
                 || (w.LifecycleStatus == LifecycleStatus.Incomplete && "incomplete".Contains(s))
diff --git a/SeaHaven.DataServices/Implementation/WorkOrderDomainJobDataService.cs b/SeaHaven.DataServices/Implementation/WorkOrderDomainJobDataService.cs
index 65d98bc..ca15639 100644
--- a/SeaHaven.DataServices/Implementation/WorkOrderDomainJobDataService.cs
+++ b/SeaHaven.DataServices/Implementation/WorkOrderDomainJobDataService.cs
@@ -120,7 +120,7 @@ namespace SeaHaven.DataServices.Implementation
                 var batch = await _context.workOrders
                     .Where(w => w.IsDeleted != true)
                     .Where(w => w.istemplate != true)
-                    .Where(w => w.ScheduledDate != null)
+                    .Where(w => w.DueDate != null)
                     .OrderBy(w => w.Id)
                     .Skip(skip)
                     .Take(batchSize)
@@ -132,7 +132,7 @@ namespace SeaHaven.DataServices.Implementation
                 foreach (var workOrder in batch)
                 {
                     examinedCount++;
-                    var shouldBePastDue = workOrder.ScheduledDate!.Value.Date < today
+                    var shouldBePastDue = workOrder.DueDate!.Value.Date < today
                         && !TerminalStatuses.Contains(workOrder.LifecycleStatus);
                     var hasFlag = workOrder.OperationalFlags.HasFlag(OperationalFlags.PastDue);
 
diff --git a/SeaHaven.Services/Helpers/WorkOrderDerivedFields.cs b/SeaHaven.Services/Helpers/WorkOrderDerivedFields.cs
index b64d16c..9cc77b9 100644
--- a/SeaHaven.Services/Helpers/WorkOrderDerivedFields.cs
+++ b/SeaHaven.Services/Helpers/WorkOrderDerivedFields.cs
@@ -6,37 +6,38 @@ namespace SeaHaven.Services.Helpers
     public static class WorkOrderDerivedFields
     {
         /// <summary>
-        /// Past due overlay — never a WorkOrderType. Matches SHOC board design.
+        /// Past due overlay from DueDate (deadline) — never a WorkOrderType.
+        /// Independent of ScheduledDate (planned work / Schedule On).
         /// </summary>
         public static bool IsPastDue(WorkOrder workOrder, DateOnly? asOf = null)
         {
             var today = asOf ?? DateOnly.FromDateTime(DateTime.UtcNow);
-            if (workOrder.ScheduledDate == null)
+            if (workOrder.DueDate == null)
                 return false;
 
             if (LifecycleStatusMapper.IsTerminal(workOrder.LifecycleStatus))
                 return false;
 
-            return DateOnly.FromDateTime(workOrder.ScheduledDate.Value.Date) < today;
+            return DateOnly.FromDateTime(workOrder.DueDate.Value.Date) < today;
         }
 
         /// <summary>
-        /// Board read-model past-due check. Phase 1 compares UTC calendar dates;
+        /// Board read-model past-due check against DueDate. Compares UTC calendar dates;
         /// business/location timezone support is planned for a later phase.
         /// </summary>
         public static bool IsPastDue(
-            DateTime? scheduledDate,
+            DateTime? dueDate,
             LifecycleStatus? lifecycleStatus,
             DateTime? utcNow = null)
         {
-            if (!scheduledDate.HasValue)
+            if (!dueDate.HasValue)
                 return false;
 
             if (LifecycleStatusMapper.IsTerminal(lifecycleStatus))
                 return false;
 
             var today = (utcNow ?? DateTime.UtcNow).Date;
-            return scheduledDate.Value.Date < today;
+            return dueDate.Value.Date < today;
         }
 
         /// <summary>
diff --git a/SeaHaven.Services/Implementation/WorkOrderBoardService.cs b/SeaHaven.Services/Implementation/WorkOrderBoardService.cs
index 04bf63c..1e840a9 100644
--- a/SeaHaven.Services/Implementation/WorkOrderBoardService.cs
+++ b/SeaHaven.Services/Implementation/WorkOrderBoardService.cs
@@ -94,7 +94,7 @@ namespace SeaHaven.Services.Implementation
                 RescheduleCount = row.RescheduleCount,
                 CarriedOver = row.CarriedOver,
                 WorkOrderType = row.WorkOrderType,
-                IsPastDue = WorkOrderDerivedFields.IsPastDue(row.ScheduledDate, row.LifecycleStatus, utcNow),
+                IsPastDue = WorkOrderDerivedFields.IsPastDue(row.DueDate, row.LifecycleStatus, utcNow),
                 SiteCode = row.SiteCode,
                 LocationName = row.LocationName,
                 PocName = row.PocName,
diff --git a/SeaHaven.Services/Implementation/WorkOrderBoardUpdateService.cs b/SeaHaven.Services/Implementation/WorkOrderBoardUpdateService.cs
index 3e8c108..e717efc 100644
--- a/SeaHaven.Services/Implementation/WorkOrderBoardUpdateService.cs
+++ b/SeaHaven.Services/Implementation/WorkOrderBoardUpdateService.cs
@@ -61,9 +61,9 @@ namespace SeaHaven.Services.Implementation
                 if (WorkOrderBoardMutationRules.IsReadOnly(workOrder.LifecycleStatus))
                     throw new WorkOrderBoardValidationException("CanceledReadOnly", "Work order is read-only in its current status.");
 
-                var isPastDue = WorkOrderDerivedFields.IsPastDue(workOrder.ScheduledDate, workOrder.LifecycleStatus);
+                var isPastDue = WorkOrderDerivedFields.IsPastDue(workOrder.DueDate, workOrder.LifecycleStatus);
                 if (WorkOrderBoardMutationRules.ShouldBlockStatusChangeWhenPastDue(canonicalField, isPastDue))
-                    throw new WorkOrderBoardValidationException("PastDueStatusBlocked", "Status cannot be changed while work order is past due. Reschedule first.");
+                    throw new WorkOrderBoardValidationException("PastDueStatusBlocked", "Status cannot be changed while work order is past due. Update due date first.");
 
                 _mutationData.SetExpectedWorkOrderVersion(workOrder, workOrderVersion);
 
@@ -232,7 +232,7 @@ namespace SeaHaven.Services.Implementation
             if (string.Equals(value.Trim(), "Overdue", StringComparison.OrdinalIgnoreCase))
                 throw new WorkOrderBoardValidationException(
                     "InvalidValue",
-                    "Overdue is not a work order type; it is derived from scheduledDate (isPastDue).");
+                    "Overdue is not a work order type; it is derived from dueDate (isPastDue).");
 
             if (!WorkOrderTypeMapper.TryParseFeLabel(value, out var parsed))
                 throw new WorkOrderBoardValidationException("InvalidValue", $"Invalid workOrderType: {value}");
diff --git a/SeaHavenIndustries.Tests/WorkOrderBoardMutationRulesTests.cs b/SeaHavenIndustries.Tests/WorkOrderBoardMutationRulesTests.cs
index 933aa80..4cda7f8 100644
--- a/SeaHavenIndustries.Tests/WorkOrderBoardMutationRulesTests.cs
+++ b/SeaHavenIndustries.Tests/WorkOrderBoardMutationRulesTests.cs
@@ -22,6 +22,8 @@ public class WorkOrderBoardMutationRulesTests
             WorkOrderBoardFieldNames.LifecycleStatus, isPastDue: true));
         Assert.False(WorkOrderBoardMutationRules.ShouldBlockStatusChangeWhenPastDue(
             WorkOrderBoardFieldNames.ScheduledDate, isPastDue: true));
+        Assert.False(WorkOrderBoardMutationRules.ShouldBlockStatusChangeWhenPastDue(
+            WorkOrderBoardFieldNames.DueDate, isPastDue: true));
     }
 
     [Fact]
diff --git a/SeaHavenIndustries.Tests/WorkOrderBoardSearchTests.cs b/SeaHavenIndustries.Tests/WorkOrderBoardSearchTests.cs
index 780c25c..510da77 100644
--- a/SeaHavenIndustries.Tests/WorkOrderBoardSearchTests.cs
+++ b/SeaHavenIndustries.Tests/WorkOrderBoardSearchTests.cs
@@ -342,7 +342,8 @@ public class WorkOrderAdvancedSearchServiceTests
             {
                 Id = 1,
                 WorkOrderType = WorkOrderType.PM,
-                ScheduledDate = today.AddDays(-3),
+                DueDate = today.AddDays(-3),
+                ScheduledDate = today.AddDays(5),
                 LifecycleStatus = LifecycleStatus.Scheduled,
                 InternalWONumber = "10000000001"
             },
@@ -358,7 +359,8 @@ public class WorkOrderAdvancedSearchServiceTests
             {
                 Id = 3,
                 WorkOrderType = WorkOrderType.Reactive,
-                ScheduledDate = today.AddDays(1),
+                DueDate = today.AddDays(1),
+                ScheduledDate = today.AddDays(-5),
                 LifecycleStatus = LifecycleStatus.Scheduled,
                 InternalWONumber = "10000000003"
             });
@@ -392,7 +394,8 @@ public class WorkOrderAdvancedSearchServiceTests
             {
                 Id = 1,
                 WorkOrderType = WorkOrderType.PM,
-                ScheduledDate = today.AddDays(-3),
+                DueDate = today.AddDays(-3),
+                ScheduledDate = today.AddDays(5),
                 LifecycleStatus = LifecycleStatus.Scheduled,
                 InternalWONumber = "10000000001"
             },
@@ -408,6 +411,7 @@ public class WorkOrderAdvancedSearchServiceTests
             {
                 Id = 3,
                 WorkOrderType = WorkOrderType.Reactive,
+                DueDate = today.AddDays(1),
                 ScheduledDate = today.AddDays(1),
                 LifecycleStatus = LifecycleStatus.Scheduled,
                 InternalWONumber = "10000000003"
@@ -444,7 +448,8 @@ public class WorkOrderAdvancedSearchServiceTests
             {
                 Id = 1,
                 WorkOrderType = WorkOrderType.Other,
-                ScheduledDate = today.AddDays(5),
+                DueDate = today.AddDays(5),
+                ScheduledDate = today.AddDays(-5),
                 LifecycleStatus = LifecycleStatus.Scheduled,
                 InternalWONumber = "10000000001"
             },
@@ -452,7 +457,8 @@ public class WorkOrderAdvancedSearchServiceTests
             {
                 Id = 2,
                 WorkOrderType = WorkOrderType.PM,
-                ScheduledDate = today.AddDays(-3),
+                DueDate = today.AddDays(-3),
+                ScheduledDate = today.AddDays(5),
                 LifecycleStatus = LifecycleStatus.Scheduled,
                 InternalWONumber = "10000000002"
             },
@@ -460,6 +466,7 @@ public class WorkOrderAdvancedSearchServiceTests
             {
                 Id = 3,
                 WorkOrderType = WorkOrderType.Reactive,
+                DueDate = today.AddDays(-2),
                 ScheduledDate = today.AddDays(-2),
                 LifecycleStatus = LifecycleStatus.Completed,
                 InternalWONumber = "10000000003"
@@ -468,6 +475,7 @@ public class WorkOrderAdvancedSearchServiceTests
             {
                 Id = 4,
                 WorkOrderType = WorkOrderType.Reactive,
+                DueDate = today.AddDays(-1),
                 ScheduledDate = today.AddDays(-1),
                 LifecycleStatus = LifecycleStatus.Canceled,
                 InternalWONumber = "10000000004"
diff --git a/SeaHavenIndustries.Tests/WorkOrderBoardServiceTests.cs b/SeaHavenIndustries.Tests/WorkOrderBoardServiceTests.cs
index 92c4d36..3eca81d 100644
--- a/SeaHavenIndustries.Tests/WorkOrderBoardServiceTests.cs
+++ b/SeaHavenIndustries.Tests/WorkOrderBoardServiceTests.cs
@@ -391,6 +391,7 @@ public class WorkOrderBoardServiceTests
         {
             Id = 1,
             InternalWONumber = "10000000001",
+            DueDate = new DateTime(2026, 6, 20),
             ScheduledDate = new DateTime(2026, 6, 24, 12, 0, 0, DateTimeKind.Utc),
             LifecycleStatus = LifecycleStatus.Scheduled
         });
diff --git a/SeaHavenIndustries.Tests/WorkOrderBoardUpdateServiceTests.cs b/SeaHavenIndustries.Tests/WorkOrderBoardUpdateServiceTests.cs
index b775ee6..7c1b678 100644
--- a/SeaHavenIndustries.Tests/WorkOrderBoardUpdateServiceTests.cs
+++ b/SeaHavenIndustries.Tests/WorkOrderBoardUpdateServiceTests.cs
@@ -91,7 +91,8 @@ public class WorkOrderBoardUpdateServiceTests
         {
             Id = 1,
             LifecycleStatus = LifecycleStatus.Scheduled,
-            ScheduledDate = DateTime.UtcNow.Date.AddDays(-3),
+            DueDate = DateTime.UtcNow.Date.AddDays(-3),
+            ScheduledDate = DateTime.UtcNow.Date.AddDays(5),
             RowVersion = new byte[] { 1, 0, 0, 0, 0, 0, 0, 1 }
         };
         context.workOrders.Add(wo);
@@ -108,6 +109,145 @@ public class WorkOrderBoardUpdateServiceTests
         Assert.Equal("PastDueStatusBlocked", ex.Code);
     }
 
+    [Fact]
+    public async Task PatchField_RescheduleAlone_DoesNotClearPastDueBlock()
+    {
+        var (context, service) = CreateSut();
+        var wo = new WorkOrder
+        {
+            Id = 1,
+            LifecycleStatus = LifecycleStatus.Scheduled,
+            DueDate = DateTime.UtcNow.Date.AddDays(-3),
+            ScheduledDate = DateTime.UtcNow.Date.AddDays(-1),
+            RowVersion = new byte[] { 1, 0, 0, 0, 0, 0, 0, 1 }
+        };
+        context.workOrders.Add(wo);
+        await context.SaveChangesAsync();
+
+        var futureSchedule = DateTime.UtcNow.Date.AddDays(7).ToString("yyyy-MM-dd");
+        var row = await service.PatchFieldAsync(1, new WorkOrderBoardPatchRequestDto
+        {
+            Field = WorkOrderBoardFieldNames.ScheduledDate,
+            Value = futureSchedule,
+            WorkOrderVersion = ToVersion(wo)
+        }, "actor-1");
+
+        Assert.True(row.IsPastDue);
+        Assert.Equal(DateTime.UtcNow.Date.AddDays(7), row.ScheduledDate!.Value.Date);
+
+        wo = await context.workOrders.SingleAsync(w => w.Id == 1);
+        var ex = await Assert.ThrowsAsync<WorkOrderBoardValidationException>(() =>
+            service.PatchFieldAsync(1, new WorkOrderBoardPatchRequestDto
+            {
+                Field = WorkOrderBoardFieldNames.LifecycleStatus,
+                Value = "Complete",
+                WorkOrderVersion = ToVersion(wo)
+            }, "actor-1"));
+
+        Assert.Equal("PastDueStatusBlocked", ex.Code);
+    }
+
+    [Fact]
+    public async Task PatchField_FutureDueDate_ClearsPastDueAndAllowsStatusChange()
+    {
+        var (context, service) = CreateSut();
+        var wo = new WorkOrder
+        {
+            Id = 1,
+            LifecycleStatus = LifecycleStatus.Scheduled,
+            DueDate = DateTime.UtcNow.Date.AddDays(-3),
+            ScheduledDate = DateTime.UtcNow.Date.AddDays(-1),
+            RowVersion = new byte[] { 1, 0, 0, 0, 0, 0, 0, 1 }
+        };
+        context.workOrders.Add(wo);
+        await context.SaveChangesAsync();
+
+        var futureDue = DateTime.UtcNow.Date.AddDays(10).ToString("yyyy-MM-dd");
+        var afterDue = await service.PatchFieldAsync(1, new WorkOrderBoardPatchRequestDto
+        {
+            Field = WorkOrderBoardFieldNames.DueDate,
+            Value = futureDue,
+            WorkOrderVersion = ToVersion(wo)
+        }, "actor-1");
+
+        Assert.False(afterDue.IsPastDue);
+        Assert.Equal(DateTime.UtcNow.Date.AddDays(-1), afterDue.ScheduledDate!.Value.Date);
+
+        wo = await context.workOrders.SingleAsync(w => w.Id == 1);
+        var afterStatus = await service.PatchFieldAsync(1, new WorkOrderBoardPatchRequestDto
+        {
+            Field = WorkOrderBoardFieldNames.LifecycleStatus,
+            Value = "Complete",
+            WorkOrderVersion = ToVersion(wo)
+        }, "actor-1");
+
+        Assert.Equal(LifecycleStatus.Completed, afterStatus.LifecycleStatus);
+        Assert.False(afterStatus.IsPastDue);
+    }
+
+    [Fact]
+    public async Task PatchField_DueDate_DoesNotChangeScheduledDate()
+    {
+        var (context, service) = CreateSut();
+        var scheduled = new DateTime(2026, 6, 20);
+        var wo = new WorkOrder
+        {
+            Id = 1,
+            LifecycleStatus = LifecycleStatus.Scheduled,
+            DueDate = new DateTime(2026, 6, 18),
+            ScheduledDate = scheduled,
+            RescheduleCount = 2,
+            RowVersion = new byte[] { 1, 0, 0, 0, 0, 0, 0, 1 }
+        };
+        context.workOrders.Add(wo);
+        await context.SaveChangesAsync();
+
+        var result = await service.PatchFieldAsync(1, new WorkOrderBoardPatchRequestDto
+        {
+            Field = WorkOrderBoardFieldNames.DueDate,
+            Value = "2026-07-01",
+            WorkOrderVersion = ToVersion(wo)
+        }, "actor-1");
+
+        Assert.Equal(new DateTime(2026, 7, 1), result.DueDate!.Value.Date);
+        Assert.Equal(scheduled, result.ScheduledDate);
+        Assert.Equal(2, result.RescheduleCount);
+
+        var persisted = await context.workOrders.SingleAsync(w => w.Id == 1);
+        Assert.Equal(scheduled, persisted.ScheduledDate);
+        Assert.Equal(2, persisted.RescheduleCount);
+    }
+
+    [Fact]
+    public async Task PatchField_ScheduledDate_DoesNotChangeDueDate()
+    {
+        var (context, service) = CreateSut();
+        var due = new DateTime(2026, 6, 18);
+        var wo = new WorkOrder
+        {
+            Id = 1,
+            LifecycleStatus = LifecycleStatus.Scheduled,
+            DueDate = due,
+            ScheduledDate = new DateTime(2026, 6, 20),
+            RowVersion = new byte[] { 1, 0, 0, 0, 0, 0, 0, 1 }
+        };
+        context.workOrders.Add(wo);
+        await context.SaveChangesAsync();
+
+        var result = await service.PatchFieldAsync(1, new WorkOrderBoardPatchRequestDto
+        {
+            Field = WorkOrderBoardFieldNames.ScheduledDate,
+            Value = "2026-06-25",
+            WorkOrderVersion = ToVersion(wo)
+        }, "actor-1");
+
+        Assert.Equal(new DateTime(2026, 6, 25), result.ScheduledDate!.Value.Date);
+        Assert.Equal(due, result.DueDate);
+
+        var persisted = await context.workOrders.SingleAsync(w => w.Id == 1);
+        Assert.Equal(due, persisted.DueDate);
+    }
+
     [Fact]
     public async Task PatchField_RejectsOverdueAsWorkOrderType()
     {
diff --git a/SeaHavenIndustries.Tests/WorkOrderDerivedFieldsTests.cs b/SeaHavenIndustries.Tests/WorkOrderDerivedFieldsTests.cs
index 0d1f61c..49b5a61 100644
--- a/SeaHavenIndustries.Tests/WorkOrderDerivedFieldsTests.cs
+++ b/SeaHavenIndustries.Tests/WorkOrderDerivedFieldsTests.cs
@@ -6,28 +6,79 @@ namespace SeaHavenIndustries.Tests;
 
 public class WorkOrderDerivedFieldsTests
 {
+    private static readonly DateOnly Today = DateOnly.FromDateTime(DateTime.UtcNow);
+    private static readonly DateTime Past = DateTime.UtcNow.Date.AddDays(-2);
+    private static readonly DateTime Future = DateTime.UtcNow.Date.AddDays(3);
+    private static readonly DateTime TodayDate = DateTime.UtcNow.Date;
+
     [Fact]
-    public void IsPastDue_WhenScheduledBeforeTodayAndNotTerminal_ReturnsTrue()
+    public void IsPastDue_WhenDuePastAndScheduleFuture_ReturnsTrue()
     {
         var wo = new WorkOrder
         {
-            ScheduledDate = DateTime.UtcNow.AddDays(-2),
+            DueDate = Past,
+            ScheduledDate = Future,
             LifecycleStatus = LifecycleStatus.Scheduled
         };
 
-        Assert.True(WorkOrderDerivedFields.IsPastDue(wo, DateOnly.FromDateTime(DateTime.UtcNow)));
+        Assert.True(WorkOrderDerivedFields.IsPastDue(wo, Today));
+        Assert.True(WorkOrderDerivedFields.IsPastDue(wo.DueDate, wo.LifecycleStatus));
     }
 
     [Fact]
-    public void IsPastDue_WhenCompleted_ReturnsFalse()
+    public void IsPastDue_WhenDueFutureAndSchedulePast_ReturnsFalse()
     {
         var wo = new WorkOrder
         {
-            ScheduledDate = DateTime.UtcNow.AddDays(-2),
-            LifecycleStatus = LifecycleStatus.Completed
+            DueDate = Future,
+            ScheduledDate = Past,
+            LifecycleStatus = LifecycleStatus.Scheduled
         };
 
-        Assert.False(WorkOrderDerivedFields.IsPastDue(wo, DateOnly.FromDateTime(DateTime.UtcNow)));
+        Assert.False(WorkOrderDerivedFields.IsPastDue(wo, Today));
+    }
+
+    [Fact]
+    public void IsPastDue_WhenDueDateNull_ReturnsFalse()
+    {
+        var wo = new WorkOrder
+        {
+            DueDate = null,
+            ScheduledDate = Past,
+            LifecycleStatus = LifecycleStatus.Scheduled
+        };
+
+        Assert.False(WorkOrderDerivedFields.IsPastDue(wo, Today));
+        Assert.False(WorkOrderDerivedFields.IsPastDue(null, LifecycleStatus.Scheduled));
+    }
+
+    [Fact]
+    public void IsPastDue_WhenDueEqualsToday_ReturnsFalse()
+    {
+        var wo = new WorkOrder
+        {
+            DueDate = TodayDate,
+            ScheduledDate = Past,
+            LifecycleStatus = LifecycleStatus.Scheduled
+        };
+
+        Assert.False(WorkOrderDerivedFields.IsPastDue(wo, Today));
+    }
+
+    [Theory]
+    [InlineData(LifecycleStatus.Completed)]
+    [InlineData(LifecycleStatus.Canceled)]
+    public void IsPastDue_WhenTerminal_ReturnsFalse(LifecycleStatus status)
+    {
+        var wo = new WorkOrder
+        {
+            DueDate = Past,
+            ScheduledDate = Past,
+            LifecycleStatus = status
+        };
+
+        Assert.False(WorkOrderDerivedFields.IsPastDue(wo, Today));
+        Assert.False(WorkOrderDerivedFields.IsPastDue(Past, status));
     }
 
     [Fact]
diff --git a/SeaHavenIndustries.Tests/WorkOrderPhase6Tests.cs b/SeaHavenIndustries.Tests/WorkOrderPhase6Tests.cs
index d6bd47e..044567b 100644
--- a/SeaHavenIndustries.Tests/WorkOrderPhase6Tests.cs
+++ b/SeaHavenIndustries.Tests/WorkOrderPhase6Tests.cs
@@ -111,7 +111,8 @@ public class WorkOrderDetailServiceTests
             Id = 1,
             InternalWONumber = "00000000001",
             LifecycleStatus = LifecycleStatus.Scheduled,
-            ScheduledDate = DateTime.UtcNow.AddDays(-2),
+            DueDate = DateTime.UtcNow.AddDays(-2),
+            ScheduledDate = DateTime.UtcNow.AddDays(3),
             Trade = "HVAC PM",
             WorkOrderType = WorkOrderType.PM,
             DocStatus = DocStatus.No,
diff --git a/SeaHavenIndustries.Tests/WorkOrderWeekRolledTests.cs b/SeaHavenIndustries.Tests/WorkOrderWeekRolledTests.cs
index bff60ca..539d4ab 100644
--- a/SeaHavenIndustries.Tests/WorkOrderWeekRolledTests.cs
+++ b/SeaHavenIndustries.Tests/WorkOrderWeekRolledTests.cs
@@ -240,12 +240,14 @@ public class WorkOrderWeekRolledTests
             new WorkOrder
             {
                 Id = 1,
+                DueDate = pastDate,
                 ScheduledDate = pastDate,
                 LifecycleStatus = LifecycleStatus.Scheduled
             },
             new WorkOrder
             {
                 Id = 2,
+                DueDate = pastDate,
                 ScheduledDate = pastDate,
                 LifecycleStatus = LifecycleStatus.Completed,
                 OperationalFlags = OperationalFlags.PastDue
@@ -253,6 +255,7 @@ public class WorkOrderWeekRolledTests
             new WorkOrder
             {
                 Id = 3,
+                DueDate = futureDate,
                 ScheduledDate = futureDate,
                 LifecycleStatus = LifecycleStatus.Scheduled,
                 OperationalFlags = OperationalFlags.PastDue
@@ -307,7 +310,8 @@ public class WorkOrderWeekRolledTests
         context.workOrders.Add(new WorkOrder
         {
             Id = 1,
-            ScheduledDate = pastDate,
+            DueDate = pastDate,
+            ScheduledDate = DateTime.UtcNow.Date.AddDays(5),
             LifecycleStatus = LifecycleStatus.Scheduled,
             OperationalFlags = OperationalFlags.None
         });
@@ -319,7 +323,7 @@ public class WorkOrderWeekRolledTests
 
         Assert.NotNull(row);
         Assert.True(row!.IsPastDue);
-        Assert.False(WorkOrderDerivedFields.IsPastDue(pastDate, LifecycleStatus.Scheduled) == false);
+        Assert.True(WorkOrderDerivedFields.IsPastDue(pastDate, LifecycleStatus.Scheduled));
     }
 
     [Fact]
@@ -331,7 +335,8 @@ public class WorkOrderWeekRolledTests
         context.workOrders.Add(new WorkOrder
         {
             Id = 1,
-            ScheduledDate = futureDate,
+            DueDate = futureDate,
+            ScheduledDate = DateTime.UtcNow.Date.AddDays(-3),
             LifecycleStatus = LifecycleStatus.Scheduled,
             OperationalFlags = OperationalFlags.PastDue
         });
diff --git a/docs/work-orders/phase-1/README.md b/docs/work-orders/phase-1/README.md
index 660bfb3..449aac5 100644
--- a/docs/work-orders/phase-1/README.md
+++ b/docs/work-orders/phase-1/README.md
@@ -88,10 +88,13 @@ Lista opções para o filtro/dropdown de assignee do board.
 ### isPastDue
 
 ```
-ScheduledDate < UTC hoje
-AND LifecycleStatus NOT IN (Complete, Canceled, Closed)
+DueDate != null
+AND DueDate < UTC hoje
+AND LifecycleStatus NOT IN (Completed, Canceled)
 ```
 
+`DueDate` null → `isPastDue = false`. Independent of `ScheduledDate` (Schedule On).
+
 Implementação: `SeaHaven.Services/Helpers/WorkOrderDerivedFields.cs`
 
 ### Vendor / Appt