diff --git a/nannyml/stats/avg/calculator.py b/nannyml/stats/avg/calculator.py
index 54942442a..7db067f71 100644
--- a/nannyml/stats/avg/calculator.py
+++ b/nannyml/stats/avg/calculator.py
@@ -97,8 +97,8 @@ def __init__(
         self._upper_alert_thresholds: Dict[str, Optional[float]] = {column_name: 0 for column_name in self.column_names}
         self._lower_alert_thresholds: Dict[str, Optional[float]] = {column_name: 0 for column_name in self.column_names}
 
-        self.lower_threshold_value_limit: float = np.nan
-        self.upper_threshold_value_limit: float = np.nan
+        self.lower_threshold_value_limit: Optional[float] = None
+        self.upper_threshold_value_limit: Optional[float] = None
         self.simple_stats_metric = 'values_avg'
 
     @log_usage(UsageEvent.STATS_AVG_FIT)
diff --git a/nannyml/stats/count/calculator.py b/nannyml/stats/count/calculator.py
index 4c4bb5813..01dbe79fa 100644
--- a/nannyml/stats/count/calculator.py
+++ b/nannyml/stats/count/calculator.py
@@ -75,8 +75,8 @@ def __init__(
         self._upper_alert_threshold: Optional[float] = 0
         self._lower_alert_threshold: Optional[float] = 0
 
-        self.lower_threshold_value_limit: float = 0
-        self.upper_threshold_value_limit: float = np.nan
+        self.lower_threshold_value_limit: Optional[float] = 0
+        self.upper_threshold_value_limit: Optional[float] = None
         self.simple_stats_metric = 'rows_count'
 
     def _calculate_count_value_stats(self, data: pd.DataFrame):
diff --git a/nannyml/stats/median/calculator.py b/nannyml/stats/median/calculator.py
index 1a5410f2a..eae5ad9e6 100644
--- a/nannyml/stats/median/calculator.py
+++ b/nannyml/stats/median/calculator.py
@@ -101,8 +101,8 @@ def __init__(
         self._upper_alert_thresholds: Dict[str, Optional[float]] = {column_name: 0 for column_name in self.column_names}
         self._lower_alert_thresholds: Dict[str, Optional[float]] = {column_name: 0 for column_name in self.column_names}
 
-        self.lower_threshold_value_limit: float = np.nan
-        self.upper_threshold_value_limit: float = np.nan
+        self.lower_threshold_value_limit: Optional[float] = None
+        self.upper_threshold_value_limit: Optional[float] = None
         self.simple_stats_metric = 'values_median'
 
     @log_usage(UsageEvent.STATS_MEDIAN_FIT)
diff --git a/nannyml/stats/std/calculator.py b/nannyml/stats/std/calculator.py
index a09da9420..c0e63db07 100644
--- a/nannyml/stats/std/calculator.py
+++ b/nannyml/stats/std/calculator.py
@@ -102,7 +102,7 @@ def __init__(
         self._upper_alert_thresholds: Dict[str, Optional[float]] = {column_name: 0 for column_name in self.column_names}
         self._lower_alert_thresholds: Dict[str, Optional[float]] = {column_name: 0 for column_name in self.column_names}
 
-        self.lower_threshold_value_limit: float = 0
+        self.lower_threshold_value_limit: Optional[float] = 0
         self.upper_threshold_value_limit: Optional[float] = None
         self.simple_stats_metric = 'values_std'
 
diff --git a/nannyml/stats/sum/calculator.py b/nannyml/stats/sum/calculator.py
index 6e5c7654d..d1b42c80b 100644
--- a/nannyml/stats/sum/calculator.py
+++ b/nannyml/stats/sum/calculator.py
@@ -96,8 +96,8 @@ def __init__(
         self._upper_alert_thresholds: Dict[str, Optional[float]] = {column_name: 0 for column_name in self.column_names}
         self._lower_alert_thresholds: Dict[str, Optional[float]] = {column_name: 0 for column_name in self.column_names}
 
-        self.lower_threshold_value_limit: float = np.nan
-        self.upper_threshold_value_limit: float = np.nan
+        self.lower_threshold_value_limit: Optional[float] = None
+        self.upper_threshold_value_limit: Optional[float] = None
         self.simple_stats_metric = 'values_sum'
 
     @log_usage(UsageEvent.STATS_SUM_FIT)