diff --git a/backend/ecmk_fetcher/excel_writer.py b/backend/ecmk_fetcher/excel_writer.py
index 089e0187..1e65cf33 100644
--- a/backend/ecmk_fetcher/excel_writer.py
+++ b/backend/ecmk_fetcher/excel_writer.py
@@ -1,5 +1,52 @@
+import os
 from typing import Any
 
+from openpyxl import Workbook, load_workbook
+from openpyxl.worksheet.worksheet import Worksheet
+
 
 def write_row(file_path: str, row_data: dict[str, Any]) -> None:
-    raise NotImplementedError
+    new_keys = list(row_data.keys())
+
+    if not os.path.exists(file_path):
+        wb = Workbook()
+        ws: Worksheet = wb.active  # type: ignore[assignment]
+        ws.append(new_keys)
+        ws.append(list(row_data.values()))
+        wb.save(file_path)
+        return
+
+    wb = load_workbook(file_path)
+    ws = wb.active  # type: ignore[assignment]
+
+    # Build a mutable header list and insert new columns using insert_cols so
+    # that existing row data shifts along with the headers.
+    headers: list[str] = [cell.value for cell in ws[1]]  # type: ignore[misc]
+
+    for key in new_keys:
+        if key in headers:
+            continue
+
+        # Find the first key that comes after this one in new_keys that already
+        # exists in headers — insert before it to keep columns logically grouped.
+        insert_before: str | None = None
+        found = False
+        for k in new_keys:
+            if k == key:
+                found = True
+                continue
+            if found and k in headers:
+                insert_before = k
+                break
+
+        if insert_before is not None:
+            col_idx = headers.index(insert_before) + 1  # 1-based
+            ws.insert_cols(col_idx)
+            ws.cell(row=1, column=col_idx, value=key)
+            headers.insert(col_idx - 1, key)
+        else:
+            headers.append(key)
+            ws.cell(row=1, column=len(headers), value=key)
+
+    ws.append([row_data.get(col) for col in headers])
+    wb.save(file_path)