diff --git a/components/form-template/auto-fill.js b/components/form-template/auto-fill.js
new file mode 100644
index 0000000..2d100ad
--- /dev/null
+++ b/components/form-template/auto-fill.js
@@ -0,0 +1,69 @@
+const DATE_ONLY_RE = /^(\d{4})-(\d{1,2})-(\d{1,2})$/;
+
+export function resolveAutoFillValue(item, form = {}) {
+  const rule = item && item.autoFill;
+  if (!rule || !rule.sourceField || !rule.type) return undefined;
+
+  const sourceValue = form ? form[rule.sourceField] : '';
+  if (!sourceValue) return '';
+
+  if (rule.type === 'addDays') {
+    const days = Number(rule.days);
+    if (!Number.isFinite(days)) return '';
+    return addDays(sourceValue, days);
+  }
+
+  return undefined;
+}
+
+export function collectAutoFillChanges(items = [], form = {}) {
+  if (!Array.isArray(items)) return [];
+
+  return items.reduce((changes, item) => {
+    if (!item || !item.title) return changes;
+
+    const nextValue = resolveAutoFillValue(item, form);
+    if (nextValue === undefined) return changes;
+
+    const currentValue = form && form[item.title] !== undefined && form[item.title] !== null
+      ? String(form[item.title])
+      : '';
+    if (currentValue !== nextValue) {
+      changes.push({ title: item.title, value: nextValue });
+    }
+    return changes;
+  }, []);
+}
+
+function addDays(value, days) {
+  const date = parseDateOnly(value);
+  if (!date) return '';
+  date.setUTCDate(date.getUTCDate() + days);
+  return formatDateOnly(date);
+}
+
+function parseDateOnly(value) {
+  const match = String(value || '').trim().match(DATE_ONLY_RE);
+  if (!match) return null;
+
+  const year = Number(match[1]);
+  const month = Number(match[2]);
+  const day = Number(match[3]);
+  const date = new Date(Date.UTC(year, month - 1, day));
+
+  if (
+    date.getUTCFullYear() !== year ||
+    date.getUTCMonth() !== month - 1 ||
+    date.getUTCDate() !== day
+  ) {
+    return null;
+  }
+  return date;
+}
+
+function formatDateOnly(date) {
+  const year = date.getUTCFullYear();
+  const month = String(date.getUTCMonth() + 1).padStart(2, '0');
+  const day = String(date.getUTCDate()).padStart(2, '0');
+  return `${year}-${month}-${day}`;
+}
diff --git a/components/form-template/index.vue b/components/form-template/index.vue
index 7b47c4f..e68671f 100644
--- a/components/form-template/index.vue
+++ b/components/form-template/index.vue
@@ -8,7 +8,7 @@
 <script setup>
 import { computed, provide, ref, watch } from 'vue';
 import verifyForm from './verify.js';
-import { collectAutoFillChanges } from './auto-fill.mjs';
+import { collectAutoFillChanges } from './auto-fill.js';
 
 import FormCell from './form-cell/index.vue';
 // import CustomCell from './custom-cell/index.vue';