diff --git a/erpnext/projects/doctype/project/project.json b/erpnext/projects/doctype/project/project.json
index b55cec332bd..ec780e63e68 100644
--- a/erpnext/projects/doctype/project/project.json
+++ b/erpnext/projects/doctype/project/project.json
@@ -121,7 +121,7 @@
    "in_list_view": 1,
    "label": "% Completed",
    "no_copy": 1,
-   "read_only": 1
+   "read_only_depends_on": "eval:doc.percent_complete_method != 'Manual'"
   },
   {
    "fieldname": "column_break_5",
@@ -484,7 +484,7 @@
  "index_web_pages_for_search": 1,
  "links": [],
  "max_attachments": 4,
- "modified": "2026-07-14 14:32:11.328347",
+ "modified": "2026-07-21 11:23:22.000000",
  "modified_by": "Administrator",
  "module": "Projects",
  "name": "Project",
diff --git a/erpnext/projects/doctype/project/project.py b/erpnext/projects/doctype/project/project.py
index 814c59525a9..981acff98c3 100644
--- a/erpnext/projects/doctype/project/project.py
+++ b/erpnext/projects/doctype/project/project.py
@@ -222,6 +222,8 @@ class Project(Document):
 		if self.percent_complete_method == "Manual":
 			if self.status == "Completed":
 				self.percent_complete = 100
+			elif flt(self.percent_complete) < 0 or flt(self.percent_complete) > 100:
+				frappe.throw(_("% Complete must be between 0 and 100"))
 			return
 
 		total = frappe.db.count("Task", dict(project=self.name))
diff --git a/erpnext/projects/doctype/project/test_project.py b/erpnext/projects/doctype/project/test_project.py
index dd10fb48ba7..56d74cb4b2e 100644
--- a/erpnext/projects/doctype/project/test_project.py
+++ b/erpnext/projects/doctype/project/test_project.py
@@ -244,6 +244,61 @@ class TestProject(ERPNextTestSuite):
 		project.save()
 		self.assertEqual(project.status, "Completed")
 
+	def _project_with_tasks(self, method, count):
+		name = f"_Test PercentComplete {frappe.generate_hash(length=8)}"
+		project = frappe.get_doc(
+			{
+				"doctype": "Project",
+				"project_name": name,
+				"status": "Open",
+				"percent_complete_method": method,
+				"company": "_Test Company",
+				"expected_start_date": nowdate(),
+			}
+		).insert()
+		task_names = []
+		for i in range(count):
+			task = frappe.get_doc(
+				{
+					"doctype": "Task",
+					"subject": f"{name} Task {i}",
+					"project": project.name,
+					"status": "Open",
+					"exp_start_date": nowdate(),
+					"exp_end_date": nowdate(),
+				}
+			).insert()
+			task_names.append(task.name)
+		return project, task_names
+
+	def test_percent_complete_manual(self):
+		project, tasks = self._project_with_tasks("Manual", 2)
+
+		# manual value is preserved on save, even with linked tasks
+		project.percent_complete = 42
+		project.save()
+		self.assertEqual(project.percent_complete, 42)
+
+		# task updates do not overwrite the manual value
+		frappe.db.set_value("Task", tasks[0], "status", "Completed")
+		project.update_percent_complete()
+		self.assertEqual(project.percent_complete, 42)
+
+		# out-of-range values are rejected
+		project.percent_complete = 150
+		self.assertRaises(frappe.ValidationError, project.save)
+		project.reload()
+
+		project.percent_complete = -10
+		self.assertRaises(frappe.ValidationError, project.save)
+		project.reload()
+
+		# Completed status forces 100 regardless of the manual value
+		project.percent_complete = 42
+		project.status = "Completed"
+		project.save()
+		self.assertEqual(project.percent_complete, 100)
+
 	def _create_portal_user(self, email):
 		"""A user with no Project-related role, so read access can only come from
 		control_access_for_project_users() sharing the doc with them."""