diff --git a/init2winit/model_lib/mdlm_rope_nanodo.py b/init2winit/model_lib/mdlm_rope_nanodo.py
index 97815764..921c6ef9 100644
--- a/init2winit/model_lib/mdlm_rope_nanodo.py
+++ b/init2winit/model_lib/mdlm_rope_nanodo.py
@@ -223,17 +223,33 @@ def _compute_elbo(self, params, batch, rng, train):
     total_loss = jnp.sum(weighted_loss_BxL)
     if pad_weights is not None:
       num_tokens = jnp.sum(pad_weights)
+      effective_num_tokens = jnp.sum(
+          is_masked_BxL.astype(jnp.float32) * pad_weights
+      )
     else:
       num_tokens = jnp.array(B * L, dtype=jnp.float32)
-    return total_loss / (num_tokens + self.hps['epsilon'])
+      effective_num_tokens = jnp.sum(is_masked_BxL.astype(jnp.float32))
+    return (
+        total_loss / (num_tokens + self.hps['epsilon']),
+        num_tokens,
+        effective_num_tokens,
+    )
 
   def evaluate_batch(self, params, batch_stats, batch):
     rng = batch['eval_rng']
-    loss = self._compute_elbo(params, batch, rng, train=False)
-    return self.metrics_bundle.single_from_model_output(normalized_loss=loss)
+    loss, num_tokens, effective_num_tokens = self._compute_elbo(
+        params, batch, rng, train=False
+    )
+    return self.metrics_bundle.single_from_model_output(
+        normalized_loss=loss,
+        num_tokens=num_tokens,
+        effective_num_tokens=effective_num_tokens,
+    )
 
   def training_cost(self, params, batch, batch_stats=None, dropout_rng=None):
-    loss = self._compute_elbo(params, batch, dropout_rng, train=True)
+    loss, num_tokens, effective_num_tokens = self._compute_elbo(
+        params, batch, dropout_rng, train=True
+    )
 
     if self.hps.get('l2_decay_factor'):
       l2_loss = model_utils.l2_regularization(
@@ -241,4 +257,7 @@ def training_cost(self, params, batch, batch_stats=None, dropout_rng=None):
       )
       loss += 0.5 * self.hps.l2_decay_factor * l2_loss
 
-    return loss, {}
+    return loss, {
+        'num_tokens': num_tokens,
+        'effective_num_tokens': effective_num_tokens,
+    }
diff --git a/init2winit/model_lib/metrics.py b/init2winit/model_lib/metrics.py
index 8f615669..c428405d 100644
--- a/init2winit/model_lib/metrics.py
+++ b/init2winit/model_lib/metrics.py
@@ -214,6 +214,48 @@ def compute(self):
     return self.count
 
 
+@flax.struct.dataclass
+class NumTokens(Metric):
+  """Computes the number of tokens seen."""
+
+  count: jnp.float32
+
+  @classmethod
+  def from_model_output(cls, num_tokens=None, **_):
+    if num_tokens is None:
+      return cls(count=jnp.array(0.0, dtype=jnp.float32))
+    return cls(count=jnp.array(num_tokens, dtype=jnp.float32))
+
+  def merge(self, other):
+    """Merges two NumTokens metrics."""
+    return type(self)(count=self.count + other.count)
+
+  def compute(self):
+    """Computes the number of tokens."""
+    return self.count
+
+
+@flax.struct.dataclass
+class EffectiveNumTokens(Metric):
+  """Computes the effective number of tokens seen (masked)."""
+
+  count: jnp.float32
+
+  @classmethod
+  def from_model_output(cls, effective_num_tokens=None, **_):
+    if effective_num_tokens is None:
+      return cls(count=jnp.array(0.0, dtype=jnp.float32))
+    return cls(count=jnp.array(effective_num_tokens, dtype=jnp.float32))
+
+  def merge(self, other):
+    """Merges two EffectiveNumTokens metrics."""
+    return type(self)(count=self.count + other.count)
+
+  def compute(self):
+    """Computes the effective number of tokens."""
+    return self.count
+
+
 # Following the Flax OGB example:
 # https://github.com/google/flax/blob/main/examples/ogbg_molpcba/train.py
 @flax.struct.dataclass
@@ -835,7 +877,10 @@ def compute(self):
         num_examples=NumExamples,
     ),
     'mdlm_metrics': Collection.create(
-        ce_loss=average_ctc_loss(), perplexity=mdlm_perplexity()
+        ce_loss=average_ctc_loss(),
+        perplexity=mdlm_perplexity(),
+        num_tokens=NumTokens,
+        effective_num_tokens=EffectiveNumTokens,
     ),
 }
 
diff --git a/init2winit/model_lib/test_metrics.py b/init2winit/model_lib/test_metrics.py
index 581d687e..fb7bbcf2 100644
--- a/init2winit/model_lib/test_metrics.py
+++ b/init2winit/model_lib/test_metrics.py
@@ -457,13 +457,17 @@ class MDLMMetricsTest(absltest.TestCase):
   """Tests for the MDLM metrics bundle."""
 
   def test_mdlm_bundle(self):
-    """MDLM bundle passes through correct ce_loss and perplexity."""
+    """MDLM bundle passes through correct metrics."""
     bundle = metrics.get_metrics('mdlm_metrics')
     result = bundle.single_from_model_output(
-        normalized_loss=jnp.float32(2.0)
+        normalized_loss=jnp.float32(2.0),
+        num_tokens=jnp.float32(100.0),
+        effective_num_tokens=jnp.float32(50.0),
     ).compute()
     np.testing.assert_allclose(result['ce_loss'], 2.0)
     np.testing.assert_allclose(result['perplexity'], jnp.exp(2.0), rtol=1e-5)
+    np.testing.assert_allclose(result['num_tokens'], 100.0)
+    np.testing.assert_allclose(result['effective_num_tokens'], 50.0)
 
 
 class MetricsBundleRegistryTest(parameterized.TestCase):