diff --git a/icu4c/source/i18n/gregoimp.cpp b/icu4c/source/i18n/gregoimp.cpp
index 161897b027a2..5a3d22ae9a38 100644
--- a/icu4c/source/i18n/gregoimp.cpp
+++ b/icu4c/source/i18n/gregoimp.cpp
@@ -86,7 +86,6 @@ double ClockMath::floorDivide(double dividend, double divisor,
             r = dividend - (quotient * divisor);
         }
     }
-    U_ASSERT(0 <= r && r < divisor);
     if (remainder != nullptr) {
         *remainder = r;
     }
@@ -204,7 +203,11 @@ void Grego::timeToFields(UDate time, int32_t& year, int8_t& month,
                         int8_t& dom, int8_t& dow, int16_t& doy, int32_t& mid, UErrorCode& status) {
     if (U_FAILURE(status)) return;
     double millisInDay;
-    double day = ClockMath::floorDivide(static_cast<double>(time), static_cast<double>(U_MILLIS_PER_DAY), &millisInDay);
+    double day = ClockMath::floorDivide(time, U_MILLIS_PER_DAY, &millisInDay);
+    if (day > INT32_MAX || day < INT32_MIN) {
+        status = U_ILLEGAL_ARGUMENT_ERROR;
+        return;
+    }
     mid = static_cast<int32_t>(millisInDay);
     dayToFields(day, year, month, dom, dow, doy, status);
 }
@@ -212,7 +215,11 @@ void Grego::timeToFields(UDate time, int32_t& year, int8_t& month,
 int32_t Grego::timeToYear(UDate time, UErrorCode& status) {
     if (U_FAILURE(status)) return 0;
     double millisInDay;
-    int32_t day = ClockMath::floorDivide(static_cast<double>(time), static_cast<double>(U_MILLIS_PER_DAY), &millisInDay);
+    double day = ClockMath::floorDivide(time, U_MILLIS_PER_DAY, &millisInDay);
+    if (day > INT32_MAX || day < INT32_MIN) {
+        status = U_ILLEGAL_ARGUMENT_ERROR;
+        return 0;
+    }
     return Grego::dayToYear(day, status);
 }
 
diff --git a/icu4c/source/i18n/simpletz.cpp b/icu4c/source/i18n/simpletz.cpp
index ec80db440938..3f3b236ea45c 100644
--- a/icu4c/source/i18n/simpletz.cpp
+++ b/icu4c/source/i18n/simpletz.cpp
@@ -520,14 +520,8 @@ SimpleTimeZone::getOffsetFromLocal(UDate date, UTimeZoneLocalOption nonExistingT
     rawOffsetGMT = getRawOffset();
     int32_t year, millis;
     int8_t month, dom, dow;
-    double dday = ClockMath::floorDivide(date, U_MILLIS_PER_DAY, &millis);
-    if (dday > INT32_MAX || dday < INT32_MIN) {
-        status = U_ILLEGAL_ARGUMENT_ERROR;
-        return;
-    }
-    int32_t day = dday;
 
-    Grego::dayToFields(day, year, month, dom, dow, status);
+    Grego::timeToFields(date, year, month, dom, dow, millis, status);
     if (U_FAILURE(status)) return;
 
     savingsDST = getOffset(GregorianCalendar::AD, year, month, dom,
@@ -555,8 +549,7 @@ SimpleTimeZone::getOffsetFromLocal(UDate date, UTimeZoneLocalOption nonExistingT
         }
     }
     if (recalc) {
-        day = ClockMath::floorDivide(date, U_MILLIS_PER_DAY, &millis);
-        Grego::dayToFields(day, year, month, dom, dow, status);
+        Grego::timeToFields(date, year, month, dom, dow, millis, status);
         if (U_FAILURE(status)) return;
         savingsDST = getOffset(GregorianCalendar::AD, year, month, dom,
                           static_cast<uint8_t>(dow), millis,
diff --git a/icu4c/source/i18n/timezone.cpp b/icu4c/source/i18n/timezone.cpp
index e2cf35992f4a..bc3a6420831e 100644
--- a/icu4c/source/i18n/timezone.cpp
+++ b/icu4c/source/i18n/timezone.cpp
@@ -732,14 +732,7 @@ void TimeZone::getOffset(UDate date, UBool local, int32_t& rawOffset,
     for (int32_t pass=0; ; ++pass) {
         int32_t year, millis;
         int8_t month, dom, dow;
-        double day = ClockMath::floorDivide(date, U_MILLIS_PER_DAY, &millis);
-
-        // out of the range
-        if (day < INT32_MIN || day > INT32_MAX) {
-            ec = U_ILLEGAL_ARGUMENT_ERROR;
-            return;
-        }
-        Grego::dayToFields(day, year, month, dom, dow, ec);
+        Grego::timeToFields(date, year, month, dom, dow, millis, ec);
         if (U_FAILURE(ec)) return;
 
         dstOffset = getOffset(GregorianCalendar::AD, year, month, dom,