diff --git a/browser/brave_stats_updater_unittest.cc b/browser/brave_stats_updater_unittest.cc
index ff1ea9aa55b..8de85e43862 100644
--- a/browser/brave_stats_updater_unittest.cc
+++ b/browser/brave_stats_updater_unittest.cc
@@ -7,6 +7,7 @@
 
 #include "base/time/time.h"
 #include "brave/browser/brave_stats_updater_params.h"
+#include "brave/browser/brave_stats_updater_util.h"
 #include "brave/common/pref_names.h"
 #include "brave/components/brave_referrals/browser/brave_referrals_service.h"
 #include "chrome/browser/browser_process.h"
@@ -285,3 +286,32 @@ TEST_F(BraveStatsUpdaterTest, HasCorrectWeekOfInstallation) {
               "2019-03-25");
   }
 }
+
+TEST_F(BraveStatsUpdaterTest, GetIsoWeekNumber) {
+  base::Time::Exploded exploded;
+  exploded.hour = 0;
+  exploded.minute = 0;
+  exploded.second = 0;
+  exploded.millisecond = 0;
+  exploded.day_of_week = 1;
+  exploded.day_of_month = 29;
+  exploded.month = 7;
+  exploded.year = 2019;
+
+  base::Time time;
+  ASSERT_TRUE(base::Time::FromLocalExploded(exploded, &time));
+  EXPECT_EQ(brave::GetIsoWeekNumber(time), 31);
+
+  exploded.day_of_month = 30;
+  exploded.month = 9;
+
+  ASSERT_TRUE(base::Time::FromLocalExploded(exploded, &time));
+  EXPECT_EQ(brave::GetIsoWeekNumber(time), 40);
+
+  exploded.day_of_month = 1;
+  exploded.month = 9;
+  exploded.day_of_week = 0;
+
+  ASSERT_TRUE(base::Time::FromLocalExploded(exploded, &time));
+  EXPECT_EQ(brave::GetIsoWeekNumber(time), 35);
+}
diff --git a/browser/brave_stats_updater_util.cc b/browser/brave_stats_updater_util.cc
index e1031db37c0..584a5edca41 100644
--- a/browser/brave_stats_updater_util.cc
+++ b/browser/brave_stats_updater_util.cc
@@ -3,6 +3,8 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this file,
  * You can obtain one at http://mozilla.org/MPL/2.0/. */
 
+#include <ctime>
+
 #include "brave/browser/brave_stats_updater_util.h"
 
 #include "base/strings/string_number_conversions.h"
@@ -44,41 +46,20 @@ std::string GetPlatformIdentifier() {
 #endif
 }
 
-int GetIsoWeekNumber(base::Time time) {
-  base::Time::Exploded now_exploded;
-  time.LocalExplode(&now_exploded);
-  now_exploded.hour = 0;
-  now_exploded.minute = 0;
-  now_exploded.second = 0;
-  now_exploded.millisecond = 0;
-  now_exploded.day_of_month =
-      now_exploded.day_of_month + 3 - ((now_exploded.day_of_week + 6) % 7);
-
-  base::Time now_adjusted;
-  if (!base::Time::FromLocalExploded(now_exploded, &now_adjusted))
-    return 0;
+int GetIsoWeekNumber(const base::Time& time) {
+  char buffer[24];
+  time_t rawtime = time.ToTimeT();
+  struct tm* timeinfo = std::localtime(&rawtime);
+  strftime(buffer, 24, "%V", timeinfo);
 
-  base::Time::Exploded jan4_exploded = {0};
-  jan4_exploded.year = now_exploded.year;
-  jan4_exploded.month = 1;
-  jan4_exploded.day_of_week = 0;
-  jan4_exploded.day_of_month = 4;
-  jan4_exploded.hour = 0;
-  jan4_exploded.minute = 0;
-  jan4_exploded.second = 0;
-  jan4_exploded.millisecond = 0;
-
-  base::Time jan4_time;
-  if (!base::Time::FromLocalExploded(jan4_exploded, &jan4_time))
+  int week_number = 0;
+  if (!base::StringToInt(buffer, &week_number))
     return 0;
 
-  return 1 + std::round(
-                 ((now_adjusted.ToJsTime() - jan4_time.ToJsTime()) / 86400000 -
-                  3 + (jan4_exploded.day_of_month + 6) % 7) /
-                 7);
+  return week_number;
 }
 
-base::Time GetYMDAsDate(base::StringPiece ymd) {
+base::Time GetYMDAsDate(const base::StringPiece& ymd) {
   const auto pieces = base::SplitStringPiece(ymd, "-", base::TRIM_WHITESPACE,
                                              base::SPLIT_WANT_NONEMPTY);
   DCHECK_EQ(pieces.size(), 3ull);
diff --git a/browser/brave_stats_updater_util.h b/browser/brave_stats_updater_util.h
index 93e5b320ed1..2a66ee68f32 100644
--- a/browser/brave_stats_updater_util.h
+++ b/browser/brave_stats_updater_util.h
@@ -19,9 +19,9 @@ std::string GetChannelName();
 
 std::string GetPlatformIdentifier();
 
-int GetIsoWeekNumber(base::Time time);
+int GetIsoWeekNumber(const base::Time& time);
 
-base::Time GetYMDAsDate(base::StringPiece ymd);
+base::Time GetYMDAsDate(const base::StringPiece& ymd);
 
 }  // namespace brave