diff --git a/docs/further.md b/docs/further.md
index ea11953..4dd78c3 100644
--- a/docs/further.md
+++ b/docs/further.md
@@ -200,6 +200,13 @@ inherit the run-specific tags. AWS Batch allows at most 50 tags per job;
 malformed pairs (missing `=` or an empty key) raise an error at submission
 time.
 
+When tags are present the plugin also sets `propagateTags=True` on
+`submit_job` so that the tags reach the underlying ECS task. Without this,
+tags are visible on the Batch job object but absent from the ECS task that
+incurs the actual EC2/ECS spend, making them invisible in Cost Explorer.
+Depending on your account's ECS tag-authorization settings, `ecs:TagResource`
+may be required on the executor role for propagation to succeed.
+
 # Pre-existing Job Definitions
 
 By default the plugin registers a fresh AWS Batch job definition for every job
diff --git a/snakemake_executor_plugin_aws_batch/__init__.py b/snakemake_executor_plugin_aws_batch/__init__.py
index 8db8e2c..0990b3f 100644
--- a/snakemake_executor_plugin_aws_batch/__init__.py
+++ b/snakemake_executor_plugin_aws_batch/__init__.py
@@ -56,8 +56,11 @@ class ExecutorSettings(ExecutorSettingsBase):
         default=None,
         metadata={
             "help": (
-                "The tags that should be applied to all of the batch tasks,"
-                "of the form KEY=VALUE"
+                "The tags that should be applied to all of the batch tasks, "
+                "of the form KEY=VALUE. Tags are propagated to the underlying ECS "
+                "tasks so that cost-allocation tags reach the actual compute spend "
+                "in Cost Explorer. Note: ecs:TagResource may be required on the "
+                "executor role depending on account ECS tagging-authorization settings."
             ),
             "env_var": False,
             "required": False,
diff --git a/snakemake_executor_plugin_aws_batch/batch_job_builder.py b/snakemake_executor_plugin_aws_batch/batch_job_builder.py
index c78f028..f7c21bf 100644
--- a/snakemake_executor_plugin_aws_batch/batch_job_builder.py
+++ b/snakemake_executor_plugin_aws_batch/batch_job_builder.py
@@ -535,14 +535,19 @@ def _submit_with_preexisting_definition(self, job_definition: str) -> dict:
         tags = self._build_job_tags()
         if tags:
             job_params["tags"] = tags
+            # Propagate tags from the Batch job to the underlying ECS task so that
+            # cost-allocation tags reach the actual compute layer. Without this,
+            # tags are visible on the Batch job object but silently absent from the
+            # ECS task that incurs the billed EC2/ECS spend.
+            # Note: ecs:TagResource may be required on the executor role depending
+            # on the account's ECS tag-authorization settings.
+            job_params["propagateTags"] = True
 
         # Mirror the optional kwargs from the dynamic path. The dynamic path bakes
         # the timeout into the registered definition; here we have no definition to
         # register, so the timeout travels as SubmitJob's top-level `timeout`
         # field, which overrides any timeout on the pre-existing definition.
         # Scheduling priority applies equally to pre-existing definitions.
-        # NOTE: any future kwarg added to submit() (e.g. propagateTags) must also
-        # be mirrored here.
         task_timeout = self._resolve_task_timeout()
         if task_timeout is not None:
             job_params["timeout"] = {"attemptDurationSeconds": task_timeout}
@@ -576,6 +581,13 @@ def submit(self):
         tags = self._build_job_tags()
         if tags:
             job_params["tags"] = tags
+            # Propagate tags from the Batch job to the underlying ECS task so that
+            # cost-allocation tags reach the actual compute layer. Without this,
+            # tags are visible on the Batch job object but silently absent from the
+            # ECS task that incurs the billed EC2/ECS spend.
+            # Note: ecs:TagResource may be required on the executor role depending
+            # on the account's ECS tag-authorization settings.
+            job_params["propagateTags"] = True
 
         priority = self._resolve_scheduling_priority()
         if priority is not None:
diff --git a/tests/test_batch_job_builder.py b/tests/test_batch_job_builder.py
index 0f9b6da..b14b401 100644
--- a/tests/test_batch_job_builder.py
+++ b/tests/test_batch_job_builder.py
@@ -255,6 +255,35 @@ def test_per_rule_queue_override_passed_to_submit_job(self):
         _, call_args = self._run_submit(builder)
         assert call_args.kwargs["jobQueue"] == "override-queue"
 
+    def test_propagate_tags_set_when_tags_present(self):
+        """propagateTags=True must be included in submit_job kwargs when tags exist."""
+        builder = _make_builder(tags={"Env": "prod"})
+        _, call_args = self._run_submit(builder)
+        assert _extract_propagate_tags(call_args) is True
+
+    def test_propagate_tags_set_when_only_env_var_tags(self):
+        """propagateTags=True must appear even when tags come only from the env var."""
+        builder = _make_builder(tags=None)
+        with patch.dict(
+            os.environ, {SNAKEMAKE_AWS_BATCH_JOB_TAGS_ENV_VAR: "Team=data"}
+        ):
+            _, call_args = self._run_submit(builder)
+        assert _extract_propagate_tags(call_args) is True
+
+    def test_propagate_tags_absent_when_no_tags(self):
+        """propagateTags must not appear in submit_job kwargs when there are no tags."""
+        builder = _make_builder(tags=None)
+        env = {
+            k: v
+            for k, v in os.environ.items()
+            if k != SNAKEMAKE_AWS_BATCH_JOB_TAGS_ENV_VAR
+        }
+        with patch.dict(os.environ, env, clear=True):
+            _, call_args = self._run_submit(builder)
+        # Assert key absence directly: an explicit propagateTags=None would also
+        # satisfy `.get(...) is None` but is not what we want to send to the SDK.
+        assert "propagateTags" not in call_args.kwargs
+
 
 def _extract_tags(call_args) -> dict | None:
     """Extract the 'tags' value from a mock call_args, or None if not present."""
@@ -265,6 +294,14 @@ def _extract_tags(call_args) -> dict | None:
     return kwargs.get("tags")
 
 
+def _extract_propagate_tags(call_args) -> bool | None:
+    """Extract the 'propagateTags' value from a mock call_args, or None if absent."""
+    if call_args is None:
+        return None
+    kwargs = call_args.kwargs if hasattr(call_args, "kwargs") else call_args[1]
+    return kwargs.get("propagateTags")
+
+
 # ---------------------------------------------------------------------------
 # Tests for _get_platform_from_queue — exception handling
 # ---------------------------------------------------------------------------
@@ -1181,6 +1218,27 @@ def test_tags_forwarded_in_preexisting_mode(self):
         builder.submit()
         call_kwargs = builder.batch_client.submit_job.call_args.kwargs
         assert call_kwargs["tags"] == {"Env": "prod", "Project": "fgumi"}
+        # propagateTags must be mirrored here just like the dynamic path so the
+        # tags reach the underlying ECS task (see submit()).
+        assert call_kwargs["propagateTags"] is True
+
+    def test_propagate_tags_absent_in_preexisting_mode_when_no_tags(self):
+        """propagateTags must not appear when there are no tags in pre-existing mode."""
+        builder = _make_builder_with_preexisting(job_definition="my-job-def")
+        builder.settings.tags = None
+        builder.batch_client.submit_job.return_value = {
+            "jobName": "snakejob-test",
+            "jobId": "abc-123",
+        }
+        env = {
+            k: v
+            for k, v in os.environ.items()
+            if k != SNAKEMAKE_AWS_BATCH_JOB_TAGS_ENV_VAR
+        }
+        with patch.dict(os.environ, env, clear=True):
+            builder.submit()
+        call_kwargs = builder.batch_client.submit_job.call_args.kwargs
+        assert "propagateTags" not in call_kwargs
 
     def test_container_overrides_no_gpu_when_zero(self):
         """GPU must NOT appear in resourceRequirements when gpu == 0."""