diff --git a/llmfoundry/callbacks/kill_loss_spike_callback.py b/llmfoundry/callbacks/kill_loss_spike_callback.py
index 12b2abaed9..3e3877d9a8 100644
--- a/llmfoundry/callbacks/kill_loss_spike_callback.py
+++ b/llmfoundry/callbacks/kill_loss_spike_callback.py
@@ -64,9 +64,9 @@ def __init__(
         self.patience = patience
         self.outlier_multiplier = outlier_multiplier
         self.outlier_counter = 0
-        self.user_defined_window_size = (window_size != _MIN_WINDOW_SIZE)
+        self.window_size_set = (window_size != _MIN_WINDOW_SIZE)
         self.window_size = window_size
-        self.loss_window = deque(maxlen=self.window_size)
+        self.loss_window = deque()
         self.user_defined_loss_cap = (loss_cap != _MAX_LOSS_CAP)
         self.loss_cap = loss_cap
 
@@ -140,21 +140,28 @@ def _handle_high_losses(self, logger: Logger) -> None:
                 window_size=self.window_size,
             )
 
-    def fit_start(self, state: State, logger: Logger) -> None:
-        # If user does not provide a window size, set window size to a fraction of the total number of training batches for the run, minimum 100 batches.
-        if not self.user_defined_window_size:
-            total_training_steps = 0
-            if state.max_duration is not None:
-                if state.max_duration.unit == TimeUnit.EPOCH and state.dataloader_len is not None:
-                    total_training_steps = state.dataloader_len * state.max_duration.value
-                elif state.max_duration.unit == TimeUnit.BATCH:
-                    total_training_steps = state.max_duration.value
-                self.window_size = max(
-                    self.window_size,
-                    round(float(total_training_steps * _WINDOW_FRACTION)),
+    def _set_window_size(self, state: State) -> None:
+        total_training_steps = 0
+        current_step = int(state.timestamp.batch)
+        current_token = int(state.timestamp.token)
+
+        if state.max_duration is not None:
+            if state.max_duration.unit == TimeUnit.EPOCH and state.dataloader_len is not None:
+                total_training_steps = state.dataloader_len * state.max_duration.value
+            elif state.max_duration.unit == TimeUnit.BATCH:
+                total_training_steps = state.max_duration.value
+            elif state.max_duration.unit == TimeUnit.TOKEN:
+                # This is an approximation of the total batches from the total tokens, assuming the ratio of tokens:batch is constant.
+                total_training_steps = current_step * (
+                    state.max_duration.value / current_token
                 )
+            self.window_size = max(
+                self.window_size,
+                round(float(total_training_steps * _WINDOW_FRACTION)),
+            )
         self.loss_window = deque(maxlen=self.window_size)
         log.info(f'Window size set to: {self.window_size}')
+        self.window_size_set = True
 
     def batch_end(self, state: State, logger: Logger) -> None:
 
@@ -166,6 +173,15 @@ def batch_end(self, state: State, logger: Logger) -> None:
         if len(self.loss_window) == self.window_size:
 
             current_step = int(state.timestamp.batch)
+
+            # If window size has not yet been set either by user or during run, set window size to a fraction of the total training duration. Minimum 100 batches.
+            if not self.window_size_set:
+                self._set_window_size(self, state)
+                # Window size has been expanded -- keep adding losses until we reach the window size.
+                if self.window_size > _MIN_WINDOW_SIZE:
+                    self.loss_window.append(train_loss)
+                    return
+
             # If user does not provide a loss cap, set loss cap to the maximum loss from the first loss window. Hard cap at loss=10.
             if not self.user_defined_loss_cap and current_step == self.window_size:
                 self.loss_cap = min(max(self.loss_window), self.loss_cap)