diff --git a/src/helpers/date-jalali.ts b/src/helpers/date-jalali.ts
index cb1eeb9..a618255 100644
--- a/src/helpers/date-jalali.ts
+++ b/src/helpers/date-jalali.ts
@@ -96,14 +96,13 @@ function jalaliPartsToGregorian(
   jMonth: number,
   jDay: number,
 ): string | null {
-  // Jalali to Julian Day Number, then to Gregorian
-  // Algorithm: https://www.fourmilab.ch/documents/calendar/
   const jy = jYear - 979;
   const jm = jMonth - 1;
   const jd = jDay - 1;
 
+  // Jalali day number — correct leap cycle is every 33 years with 8 leaps
   let jDayNo =
-    365 * jy + Math.floor(jy / 4) - Math.floor(jy / 100) + Math.floor(jy / 400);
+    365 * jy + Math.floor(jy / 33) * 8 + Math.floor(((jy % 33) + 3) / 4);
 
   const jalaliMonthDays = [31, 31, 31, 31, 31, 31, 30, 30, 30, 30, 30, 29];
   for (let i = 0; i < jm; i++) {
@@ -111,29 +110,29 @@ function jalaliPartsToGregorian(
   }
   jDayNo += jd;
 
-  // Convert to Gregorian day number (offset from 1970-01-01 in Julian days)
-  const gDayNo = jDayNo + 79;
+  // Offset to Gregorian day number anchored at 1600
+  let gDayNo = jDayNo + 79;
 
-  let gy = 1979 + 400 * Math.floor(gDayNo / 146097);
-  let days = gDayNo % 146097;
+  let gy = 1600 + 400 * Math.floor(gDayNo / 146097);
+  gDayNo %= 146097;
 
   let leap = true;
-  if (days >= 36525) {
-    days--;
-    gy += 100 * Math.floor(days / 36524);
-    days %= 36524;
-    if (days >= 365) days++;
+  if (gDayNo >= 36525) {
+    gDayNo--;
+    gy += 100 * Math.floor(gDayNo / 36524);
+    gDayNo %= 36524;
+    if (gDayNo >= 365) gDayNo++;
     else leap = false;
   }
 
-  gy += 4 * Math.floor(days / 1461);
-  days %= 1461;
+  gy += 4 * Math.floor(gDayNo / 1461);
+  gDayNo %= 1461;
 
-  if (days >= 366) {
+  if (gDayNo >= 366) {
     leap = false;
-    days--;
-    gy += Math.floor(days / 365);
-    days %= 365;
+    gDayNo--;
+    gy += Math.floor(gDayNo / 365);
+    gDayNo %= 365;
   }
 
   const gregorianMonthDays = [
@@ -153,19 +152,18 @@ function jalaliPartsToGregorian(
 
   let gm = 0;
   for (let i = 0; i < 12; i++) {
-    if (days < gregorianMonthDays[i]) {
+    if (gDayNo < gregorianMonthDays[i]) {
       gm = i + 1;
       break;
     }
-    days -= gregorianMonthDays[i];
+    gDayNo -= gregorianMonthDays[i];
   }
-  const gd = days + 1;
+  const gd = gDayNo + 1;
 
   const mm = String(gm).padStart(2, "0");
   const dd = String(gd).padStart(2, "0");
   const result = `${gy}-${mm}-${dd}`;
 
-  // Sanity check
   const check = new Date(result);
   if (isNaN(check.getTime())) return null;
 
diff --git a/src/sand-hub/sand-hub.service.ts b/src/sand-hub/sand-hub.service.ts
index 801cb07..b156e41 100644
--- a/src/sand-hub/sand-hub.service.ts
+++ b/src/sand-hub/sand-hub.service.ts
@@ -564,6 +564,7 @@ export class SandHubService {
       const requestUrl = `${process.env.SANHUB_BASE_URL}/personal-inquiry/tejarat-no`;
 
       const gregorianBirthdate = jalaliToGregorianDate(birthDate);
+      console.log(gregorianBirthdate);
       if (!gregorianBirthdate) {
         throw new BadRequestException(
           `Invalid birth date for personal inquiry: ${birthDate}. Expected a Jalali date (e.g. 13770624 or "1377-06-24").`,