diff --git a/datajunction-clients/python/datajunction/deployment.py b/datajunction-clients/python/datajunction/deployment.py
index dd694a8ac..30969e723 100644
--- a/datajunction-clients/python/datajunction/deployment.py
+++ b/datajunction-clients/python/datajunction/deployment.py
@@ -297,11 +297,18 @@ def get_impact(
         """
         console = console or self.console
         deployment_spec, file_errors = self._reconstruct_deployment_spec(source_path)
-        deployment_spec["namespace"] = namespace or deployment_spec.get("namespace")
+        base_namespace = deployment_spec.get("namespace") or ""
         source = deployment_spec.get("source", {})
         branch = os.getenv("DJ_DEPLOY_BRANCH") or DeploymentService._detect_git_branch(
             cwd=source_path,
         )
+        if namespace:
+            deployment_spec["namespace"] = namespace
+        elif branch and base_namespace:
+            deployment_spec["namespace"] = DeploymentService._derive_namespace(
+                base_namespace,
+                branch,
+            )
         if display:
             print_deployment_header(
                 mode="dry run",
diff --git a/datajunction-clients/python/tests/test_cli.py b/datajunction-clients/python/tests/test_cli.py
index e6e939020..800c6c3f1 100644
--- a/datajunction-clients/python/tests/test_cli.py
+++ b/datajunction-clients/python/tests/test_cli.py
@@ -1008,6 +1008,8 @@ def test_push_with_repo_flag_sets_env_var(
             "dj",
             "push",
             "./deploy0",
+            "--namespace",
+            "repo_flag_test",
             "--repo",
             "github.com/test/repo",
         ]
diff --git a/datajunction-clients/python/tests/test_deploy.py b/datajunction-clients/python/tests/test_deploy.py
index 709fee5de..3028e113c 100644
--- a/datajunction-clients/python/tests/test_deploy.py
+++ b/datajunction-clients/python/tests/test_deploy.py
@@ -1197,6 +1197,35 @@ def test_get_impact_with_namespace_override(self, tmp_path, monkeypatch):
         call_args = mock_client.get_deployment_impact.call_args[0][0]
         assert call_args["namespace"] == "override.ns"
 
+    def test_get_impact_derives_namespace_from_git_branch(self, tmp_path, monkeypatch):
+        """get_impact should derive namespace from git branch, same as push."""
+        (tmp_path / "dj.yaml").write_text(yaml.safe_dump({"namespace": "project"}))
+        (tmp_path / "my_node.yaml").write_text(
+            yaml.safe_dump({"name": "project.my_node"}),
+        )
+
+        monkeypatch.delenv("DJ_DEPLOY_REPO", raising=False)
+        monkeypatch.delenv("DJ_DEPLOY_BRANCH", raising=False)
+        monkeypatch.setattr(
+            "datajunction.deployment.subprocess.run",
+            lambda *a, **kw: mock.MagicMock(stdout="feature/new-metric\n"),
+        )
+
+        mock_client = MagicMock()
+        mock_client.get_deployment_impact.return_value = {
+            "uuid": "dry_run",
+            "namespace": "project.feature_new_metric",
+            "status": "success",
+            "results": [],
+            "downstream_impacts": [],
+        }
+
+        svc = DeploymentService(mock_client, console=Console(file=io.StringIO()))
+        svc.get_impact(tmp_path)
+
+        call_args = mock_client.get_deployment_impact.call_args[0][0]
+        assert call_args["namespace"] == "project.feature_new_metric"
+
 
 class TestDetectGitBranch:
     """Tests for _detect_git_branch."""