diff --git a/renderers/angular/src/lib/catalog/datetime-input.ts b/renderers/angular/src/lib/catalog/datetime-input.ts
index 61a679be9..e4487f8f2 100644
--- a/renderers/angular/src/lib/catalog/datetime-input.ts
+++ b/renderers/angular/src/lib/catalog/datetime-input.ts
@@ -94,7 +94,8 @@ export class DatetimeInput extends DynamicComponent {
     }
 
     const year = this.padNumber(date.getFullYear());
-    const month = this.padNumber(date.getMonth());
+    // getMonth() is 0-indexed (0=Jan), but standard date format requires 1-indexed (01=Jan).
+    const month = this.padNumber(date.getMonth() + 1);
     const day = this.padNumber(date.getDate());
     const hours = this.padNumber(date.getHours());
     const minutes = this.padNumber(date.getMinutes());
diff --git a/renderers/lit/src/0.8/ui/datetime-input.ts b/renderers/lit/src/0.8/ui/datetime-input.ts
index e7b6171c8..083ca1a68 100644
--- a/renderers/lit/src/0.8/ui/datetime-input.ts
+++ b/renderers/lit/src/0.8/ui/datetime-input.ts
@@ -134,7 +134,8 @@ export class DateTimeInput extends Root {
     }
 
     const year = this.#padNumber(date.getFullYear());
-    const month = this.#padNumber(date.getMonth());
+    // getMonth() is 0-indexed (0=Jan), but standard date format requires 1-indexed (01=Jan).
+    const month = this.#padNumber(date.getMonth() + 1);
     const day = this.#padNumber(date.getDate());
     const hours = this.#padNumber(date.getHours());
     const minutes = this.#padNumber(date.getMinutes());