diff --git a/src/bootstrap_datepicker_plus/_base.py b/src/bootstrap_datepicker_plus/_base.py
index 7e83fe0..30cae46 100644
--- a/src/bootstrap_datepicker_plus/_base.py
+++ b/src/bootstrap_datepicker_plus/_base.py
@@ -14,8 +14,8 @@ class BasePickerInput(DateTimeBaseInput):
     """Base Date-Picker input class for widgets of this package."""
 
     variant = WidgetVariant.date
+    _date_format = "%Y-%m-%d"
     backend_date_format = "YYYY-MM-DD"
-    format_key = "DATE_INPUT_FORMATS"
     options: Optional[WidgetOptions] = None
     template_name = "bootstrap_datepicker_plus/input.html"
 
@@ -53,7 +53,7 @@ def __init__(
             self.options,
             options,
         )
-        super().__init__(attrs)
+        super().__init__(attrs, self._date_format)
 
     def build_attrs(
         self, base_attrs: InputAttrs, extra_attrs: Optional[InputAttrs] = None
diff --git a/src/bootstrap_datepicker_plus/widgets.py b/src/bootstrap_datepicker_plus/widgets.py
index 6a686cc..c8f3eef 100644
--- a/src/bootstrap_datepicker_plus/widgets.py
+++ b/src/bootstrap_datepicker_plus/widgets.py
@@ -21,29 +21,29 @@ class TimePickerInput(BasePickerInput):
     """Widget to display a Time-Picker Calendar on a TimeField."""
 
     variant = WidgetVariant.time
+    _date_format = "%H:%M:%S"
     backend_date_format = "HH:mm:ss"
-    format_key = "TIME_INPUT_FORMATS"
 
 
 class DateTimePickerInput(BasePickerInput):
     """Widget to display a DateTime-Picker Calendar on a DateTimeField."""
 
     variant = WidgetVariant.datetime
+    _date_format = "%Y-%m-%d %H:%M:%S"
     backend_date_format = "YYYY-MM-DD HH:mm:ss"
-    format_key = "DATETIME_INPUT_FORMATS"
 
 
 class MonthPickerInput(BasePickerInput):
     """Widget to display a Month-Picker Calendar on a DateField."""
 
     variant = WidgetVariant.month
+    _date_format = "%Y-%m-%d"
     backend_date_format = "YYYY-MM-01"
-    format_key = "DATE_INPUT_FORMATS"
 
 
 class YearPickerInput(BasePickerInput):
     """Widget to display a Year-Picker Calendar on a DateField."""
 
     variant = WidgetVariant.year
+    _date_format = "%Y-%m-%d"
     backend_date_format = "YYYY-01-01"
-    format_key = "DATE_INPUT_FORMATS"