diff --git a/CHANGELOG.adoc b/CHANGELOG.adoc
index d8a83e9..939df00 100644
--- a/CHANGELOG.adoc
+++ b/CHANGELOG.adoc
@@ -18,6 +18,7 @@
 - https://github.com/ObeoNetwork/pepper/issues/18[#18] Enhance the ergonomy of contextual menu in Gantt
 - https://github.com/ObeoNetwork/pepper/issues/49[#49] Rework the detail views of Task and Workpackage
 - https://github.com/ObeoNetwork/pepper/issues/55[#55] Link detail view updates with Gantt view
+- https://github.com/ObeoNetwork/pepper/issues/42[#42] Change behavior for start and end dates of a work package
 
 === Bug fixes
 
diff --git a/backend/pepper-mm/src/main/java/pepper/peppermm/impl/WorkpackageImpl.java b/backend/pepper-mm/src/main/java/pepper/peppermm/impl/WorkpackageImpl.java
index 0692554..d432fc6 100644
--- a/backend/pepper-mm/src/main/java/pepper/peppermm/impl/WorkpackageImpl.java
+++ b/backend/pepper-mm/src/main/java/pepper/peppermm/impl/WorkpackageImpl.java
@@ -12,8 +12,10 @@
  ******************************************************************************/
 package pepper.peppermm.impl;
 
+import java.time.Instant;
 import java.time.LocalDate;
 
+import java.time.ZoneId;
 import java.time.temporal.ChronoUnit;
 import java.util.Collection;
 
@@ -367,13 +369,45 @@ public void setDescription(String newDescription) {
     /**
      * <!-- begin-user-doc --> <!-- end-user-doc -->
      * 
-     * @generated
+     * @generated NOT
      */
     @Override
     public LocalDate getStartDate() {
+        if (ownedTasks != null && !ownedTasks.isEmpty()) {
+            Instant oldestInstant = null;
+            for (Task task : ownedTasks) {
+                Instant newOldestInstant = getOldestInstant(task, null);
+                if (oldestInstant == null || (newOldestInstant != null && newOldestInstant.isBefore(oldestInstant))) {
+                    oldestInstant = newOldestInstant;
+                }
+            }
+            if (oldestInstant != null) {
+                return LocalDate.ofInstant(oldestInstant, ZoneId.systemDefault());
+            }
+        }
         return startDate;
     }
 
+    /**
+     * <!-- begin-user-doc --> <!-- end-user-doc -->
+     *
+     * @generated NOT
+     */
+    private Instant getOldestInstant(Task task, Instant oldestInstant) {
+        Instant startTime = task.getStartTime();
+
+        if (startTime != null && (oldestInstant == null || startTime.isBefore(oldestInstant))) {
+            oldestInstant = startTime;
+        }
+
+        if (task.getSubTasks() != null) {
+            for (Task subTask : task.getSubTasks()) {
+                oldestInstant = getOldestInstant(subTask, oldestInstant);
+            }
+        }
+        return oldestInstant;
+    }
+
     /**
      * If the workpackage's {@code startDate} is constrained by {@code START_END}, it is not changed
      * 
@@ -406,13 +440,45 @@ public void setStartDate(LocalDate newStartDate) {
     /**
      * <!-- begin-user-doc --> <!-- end-user-doc -->
      * 
-     * @generated
+     * @generated NOT
      */
     @Override
     public LocalDate getEndDate() {
+        if (ownedTasks != null && !ownedTasks.isEmpty()) {
+            Instant latestInstant = null;
+            for (Task task : ownedTasks) {
+                Instant newLattestInstant = getLatestInstant(task, null);
+                if (latestInstant == null || (newLattestInstant != null && newLattestInstant.isAfter(latestInstant))) {
+                    latestInstant = newLattestInstant;
+                }
+            }
+            if (latestInstant != null) {
+                return LocalDate.ofInstant(latestInstant, ZoneId.systemDefault());
+            }
+        }
         return endDate;
     }
 
+    /**
+     * <!-- begin-user-doc --> <!-- end-user-doc -->
+     *
+     * @generated NOT
+     */
+    private Instant getLatestInstant(Task task, Instant latestInstant) {
+        Instant endTime = task.getEndTime();
+
+        if (endTime != null && (latestInstant == null || endTime.isAfter(latestInstant))) {
+            latestInstant = endTime;
+        }
+
+        if (task.getSubTasks() != null) {
+            for (Task subTask : task.getSubTasks()) {
+                latestInstant = getLatestInstant(subTask, latestInstant);
+            }
+        }
+        return latestInstant;
+    }
+
     /**
      * If the workpackage's {@code endDate} is constrained by {@code START_END}, it is not changed
      * 
diff --git a/backend/pepper-starter/src/main/java/pepper/starter/services/WorkpackagePropertiesConfigurer.java b/backend/pepper-starter/src/main/java/pepper/starter/services/WorkpackagePropertiesConfigurer.java
index 5548028..f97be65 100644
--- a/backend/pepper-starter/src/main/java/pepper/starter/services/WorkpackagePropertiesConfigurer.java
+++ b/backend/pepper-starter/src/main/java/pepper/starter/services/WorkpackagePropertiesConfigurer.java
@@ -290,7 +290,10 @@ private TextfieldDescription getDurationWidget() {
         String id = "workpackage.duration";
         return TextfieldDescription.newTextfieldDescription(id)
                 .isReadOnlyProvider(vm -> vm.get(VariableManager.SELF, Workpackage.class)
-                        .map(workpackage -> workpackage.getCalculationOption() == TaskTimeBoundariesConstraint.START_END || isDateOptionForced(workpackage))
+                        .map(workpackage -> workpackage.getCalculationOption() == TaskTimeBoundariesConstraint.START_END
+                                || isDateOptionForced(workpackage)
+                                || !workpackage.getOwnedTasks().isEmpty()
+                        )
                         .orElse(true))
                 .idProvider(variableManager -> id)
                 .targetObjectIdProvider(this.propertiesConfigurerService.getSemanticTargetIdProvider())
@@ -357,36 +360,6 @@ private ReferenceWidgetDescription getDependenciesWidget() {
                 .build();
     }
 
-    private Optional<Object> getItem(VariableManager variableManager) {
-        return variableManager.get(ReferenceWidgetComponent.ITEM_VARIABLE, Object.class);
-    }
-
-    private List<?> getReferenceValue(VariableManager variableManager, Object feature) {
-        List<?> value = List.of();
-        EStructuralFeature.Setting setting = this.resolveSetting(variableManager, feature);
-        if (setting != null) {
-            var rawValue = setting.get(true);
-            if (setting.getEStructuralFeature().isMany()) {
-                value = (List<?>) rawValue;
-            } else if (rawValue != null) {
-                value = List.of(rawValue);
-            } else {
-                value = List.of();
-            }
-        }
-        return value;
-    }
-
-    private EStructuralFeature.Setting resolveSetting(VariableManager variableManager, Object feature) {
-        EObject referenceOwner = variableManager.get(VariableManager.SELF, EObject.class).orElse(null);
-        if (referenceOwner != null && feature instanceof EReference reference) {
-            return ((InternalEObject) referenceOwner).eSetting(reference);
-        } else {
-            return null;
-        }
-    }
-
-
     private DateTimeDescription getStartDateWidget() {
         Function<VariableManager, String> valueProvider = variableManager -> variableManager.get(VariableManager.SELF, Workpackage.class)
                 .map(workpackage -> {
@@ -421,7 +394,11 @@ private DateTimeDescription getStartDateWidget() {
         String id = "workpackage.startTime";
         return DateTimeDescription.newDateTimeDescription(id)
                 .isReadOnlyProvider(vm -> vm.get(VariableManager.SELF, Workpackage.class)
-                        .map(workpackage -> workpackage.getCalculationOption() == TaskTimeBoundariesConstraint.END_DURATION || isDateOptionForced(workpackage) || isPointed(workpackage, StartOrEnd.START))
+                        .map(workpackage -> workpackage.getCalculationOption() == TaskTimeBoundariesConstraint.END_DURATION
+                                || isDateOptionForced(workpackage)
+                                || isPointed(workpackage, StartOrEnd.START)
+                                || !workpackage.getOwnedTasks().isEmpty()
+                                )
                         .orElse(true))
                 .idProvider(variableManager -> id)
                 .targetObjectIdProvider(this.propertiesConfigurerService.getSemanticTargetIdProvider())
@@ -469,7 +446,11 @@ private DateTimeDescription getEndDateWidget() {
         String id = "workpackage.endTime";
         return DateTimeDescription.newDateTimeDescription(id)
                 .isReadOnlyProvider(vm -> vm.get(VariableManager.SELF, Workpackage.class)
-                        .map(workpackage -> workpackage.getCalculationOption() == TaskTimeBoundariesConstraint.START_DURATION || isDateOptionForced(workpackage) || isPointed(workpackage, StartOrEnd.END))
+                        .map(workpackage -> workpackage.getCalculationOption() == TaskTimeBoundariesConstraint.START_DURATION
+                                || isDateOptionForced(workpackage)
+                                || isPointed(workpackage, StartOrEnd.END)
+                                || !workpackage.getOwnedTasks().isEmpty()
+                        )
                         .orElse(true))
                 .idProvider(variableManager -> id)
                 .targetObjectIdProvider(this.propertiesConfigurerService.getSemanticTargetIdProvider())
@@ -497,6 +478,35 @@ private Boolean isPointed(Workpackage workpackage, StartOrEnd startOrEnd) {
         return false;
     }
 
+    private Optional<Object> getItem(VariableManager variableManager) {
+        return variableManager.get(ReferenceWidgetComponent.ITEM_VARIABLE, Object.class);
+    }
+
+    private List<?> getReferenceValue(VariableManager variableManager, Object feature) {
+        List<?> value = List.of();
+        EStructuralFeature.Setting setting = this.resolveSetting(variableManager, feature);
+        if (setting != null) {
+            var rawValue = setting.get(true);
+            if (setting.getEStructuralFeature().isMany()) {
+                value = (List<?>) rawValue;
+            } else if (rawValue != null) {
+                value = List.of(rawValue);
+            } else {
+                value = List.of();
+            }
+        }
+        return value;
+    }
+
+    private EStructuralFeature.Setting resolveSetting(VariableManager variableManager, Object feature) {
+        EObject referenceOwner = variableManager.get(VariableManager.SELF, EObject.class).orElse(null);
+        if (referenceOwner != null && feature instanceof EReference reference) {
+            return ((InternalEObject) referenceOwner).eSetting(reference);
+        } else {
+            return null;
+        }
+    }
+
     private Function<VariableManager, List<?>> getPersonsProvider() {
         return variableManager -> variableManager.get(VariableManager.SELF, EObject.class)
                 .map(EObject::eResource)