diff --git a/esphome/components/api/api_pb2.cpp b/esphome/components/api/api_pb2.cpp
index 6db5dcf97e..038c1c7800 100644
--- a/esphome/components/api/api_pb2.cpp
+++ b/esphome/components/api/api_pb2.cpp
@@ -2353,12 +2353,11 @@ uint32_t BluetoothLERawAdvertisementsResponse::calculate_size() const {
   uint32_t size = 0;
   for (uint16_t i = 0; i < this->advertisements_len; i++) {
     auto &sub_msg = this->advertisements[i];
-    uint32_t sub_size = 0;
-    sub_size += ProtoSize::calc_uint64_force(1, sub_msg.address);
-    sub_size += ProtoSize::calc_sint32_force(1, sub_msg.rssi);
-    sub_size += sub_msg.address_type ? 2 : 0;
-    sub_size += 2 + sub_msg.data_len;
-    size += 2 + sub_size;
+    size += 2;
+    size += ProtoSize::calc_uint64_force(1, sub_msg.address);
+    size += ProtoSize::calc_sint32_force(1, sub_msg.rssi);
+    size += sub_msg.address_type ? 2 : 0;
+    size += 2 + sub_msg.data_len;
   }
   return size;
 }
diff --git a/script/api_protobuf/api_protobuf.py b/script/api_protobuf/api_protobuf.py
index 6f92e4cb6d..746402f8c6 100755
--- a/script/api_protobuf/api_protobuf.py
+++ b/script/api_protobuf/api_protobuf.py
@@ -1628,7 +1628,8 @@ def _generate_inline_size_block(
 
     lines = []
     lines.append(f"auto &sub_msg = {element};")
-    lines.append("uint32_t sub_size = 0;")
+    # 1 byte tag + 1 byte length (guaranteed < 128 by validation)
+    lines.append("size += 2;")
 
     for field in sub_desc.field:
         if field.options.deprecated:
@@ -1636,14 +1637,10 @@ def _generate_inline_size_block(
         ti = create_field_type_info(field, needs_decode=False, needs_encode=True)
         force = get_field_opt(field, pb.force, False)
         size_line = ti.get_size_calculation(f"sub_msg.{ti.field_name}", force)
-        # Replace "size +=" with "sub_size +=" for the local accumulator
-        size_line = size_line.replace("size +=", "sub_size +=")
         # Replace hardcoded this-> references (e.g., FixedArrayBytesType uses this->field_len)
         size_line = size_line.replace("this->", "sub_msg.")
         lines.extend(size_line.split("\n"))
 
-    # 1 byte tag + 1 byte length (guaranteed < 128) + body
-    lines.append("size += 2 + sub_size;")
     return "\n".join(lines)