diff --git a/stl/inc/chrono b/stl/inc/chrono
index 7927b883277..25d3b2ac196 100644
--- a/stl/inc/chrono
+++ b/stl/inc/chrono
@@ -1394,35 +1394,31 @@ namespace chrono {
         // courtesy of Howard Hinnant
         // https://howardhinnant.github.io/date_algorithms.html#civil_from_days
         _NODISCARD static constexpr year_month_day _Civil_from_days(int _Tp) noexcept {
-            static_assert(numeric_limits<unsigned int>::digits >= 18);
-            static_assert(numeric_limits<int>::digits >= 20);
-            const int _Zx                  = _Tp + 719468; // Shift epoch to 0000-03-01
-            const int _Era                 = (_Zx >= 0 ? _Zx : _Zx - 146096) / 146097;
-            const unsigned int _Day_of_era = static_cast<unsigned int>(_Zx - _Era * 146097); // [0, 146096]
-            const unsigned int _Year_of_era =
-                (_Day_of_era - _Day_of_era / 1460 + _Day_of_era / 36524 - _Day_of_era / 146096) / 365; // [0, 399]
-            const int _Year = static_cast<int>(_Year_of_era) + _Era * 400; // Where March is the first month
-            const unsigned int _Day_of_year =
-                _Day_of_era - (365 * _Year_of_era + _Year_of_era / 4 - _Year_of_era / 100); // [0, 365]
-            const unsigned int _Mp    = (5 * _Day_of_year + 2) / 153; // [0, 11]
-            const unsigned int _Day   = _Day_of_year - (153 * _Mp + 2) / 5 + 1; // [1, 31]
-            const unsigned int _Month = _Mp + (_Mp < 10 ? 3 : static_cast<unsigned int>(-9)); // [1, 12]
+            static_assert(numeric_limits<unsigned int>::digits >= 32);
+            static_assert(numeric_limits<int>::digits >= 26);
+            const int _Zx      = _Tp + 719468; // Shift epoch to 0000-03-01
+            const int _Century = (_Zx >= 0 ? 4 * _Zx + 3 : 4 * _Zx - 146093) / 146097;
+            const unsigned int _Day_of_century =
+                static_cast<unsigned int>(_Zx - ((146097 * _Century) >> 2)); // [0, 36524]
+            const unsigned int _Year_of_century = (91867 * (_Day_of_century + 1)) >> 25; // [0, 99]
+            const int _Year = static_cast<int>(_Year_of_century) + _Century * 100; // Where March is the first month
+            const unsigned int _Day_of_year = _Day_of_century - ((1461 * _Year_of_century) >> 2); // [0, 365]
+            const unsigned int _Mp          = (535 * _Day_of_year + 333) >> 14; // [0, 11]
+            const unsigned int _Day         = _Day_of_year - ((979 * _Mp + 19) >> 5) + 1; // [1, 31]
+            const unsigned int _Month       = _Mp + (_Mp < 10 ? 3 : static_cast<unsigned int>(-9)); // [1, 12]
             return year_month_day{_CHRONO year{_Year + (_Month <= 2)}, _CHRONO month{_Month}, _CHRONO day{_Day}};
         }
         // courtesy of Howard Hinnant
         // https://howardhinnant.github.io/date_algorithms.html#days_from_civil
         _NODISCARD constexpr days _Days_from_civil() const noexcept {
             static_assert(numeric_limits<unsigned int>::digits >= 18);
-            static_assert(numeric_limits<int>::digits >= 20);
-            const int _Ye                   = static_cast<int>(_Year) - (_Month <= _CHRONO month{2});
-            const unsigned int _Mo          = static_cast<unsigned int>(_Month);
-            const int _Era                  = (_Ye >= 0 ? _Ye : _Ye - 399) / 400;
-            const unsigned int _Year_of_era = static_cast<unsigned int>(_Ye - _Era * 400); // [0, 399]
-            const unsigned int _Day_of_year = (153 * (_Mo + (_Mo > 2 ? static_cast<unsigned int>(-3) : 9)) + 2) / 5
-                                            + static_cast<unsigned int>(_Day) - 1; // [0, 365]
-            const unsigned int _Day_of_era =
-                _Year_of_era * 365 + _Year_of_era / 4 - _Year_of_era / 100 + _Day_of_year; // [0, 146096]
-            return days{_Era * 146097 + static_cast<int>(_Day_of_era) - 719468};
+            static_assert(numeric_limits<int>::digits >= 26);
+            const unsigned int _Mo = static_cast<unsigned int>(_Month); // [1, 12]
+            const int _Ye          = static_cast<int>(_Year) - (_Mo <= 2);
+            const int _Century     = (_Ye >= 0 ? _Ye : _Ye - 99) / 100;
+            const unsigned int _Mp = _Mo + (_Mo > 2 ? static_cast<unsigned int>(-3) : 9); // [0, 11]
+            const int _Day_of_year = static_cast<int>(((979 * _Mp + 19) >> 5) + static_cast<unsigned int>(_Day)) - 1;
+            return days{((_Ye * 1461) >> 2) - _Century + (_Century >> 2) + _Day_of_year - 719468};
         }
     };
 
diff --git a/tests/std/tests/P0355R7_calendars_and_time_zones_dates/test.cpp b/tests/std/tests/P0355R7_calendars_and_time_zones_dates/test.cpp
index 90d6d7ad946..4bb31c8a863 100644
--- a/tests/std/tests/P0355R7_calendars_and_time_zones_dates/test.cpp
+++ b/tests/std/tests/P0355R7_calendars_and_time_zones_dates/test.cpp
@@ -700,6 +700,190 @@ constexpr void year_month_day_test() {
             }
         }
     }
+
+    if (is_constant_evaluated()) {
+        // clang-format off
+        static_assert(sys_days{  2000y/ 1/ 1} == sys_days{days{    10957}});
+        static_assert(sys_days{  2000y/ 1/31} == sys_days{days{    10987}});
+        static_assert(sys_days{  2000y/ 2/ 1} == sys_days{days{    10988}});
+        static_assert(sys_days{  2000y/ 2/29} == sys_days{days{    11016}});
+        static_assert(sys_days{  2000y/ 3/ 1} == sys_days{days{    11017}});
+        static_assert(sys_days{  2000y/ 3/31} == sys_days{days{    11047}});
+        static_assert(sys_days{  2000y/ 4/ 1} == sys_days{days{    11048}});
+        static_assert(sys_days{  2000y/ 4/30} == sys_days{days{    11077}});
+        static_assert(sys_days{  2000y/ 5/ 1} == sys_days{days{    11078}});
+        static_assert(sys_days{  2000y/ 5/31} == sys_days{days{    11108}});
+        static_assert(sys_days{  2000y/ 6/ 1} == sys_days{days{    11109}});
+        static_assert(sys_days{  2000y/ 6/30} == sys_days{days{    11138}});
+        static_assert(sys_days{  2000y/ 7/ 1} == sys_days{days{    11139}});
+        static_assert(sys_days{  2000y/ 7/31} == sys_days{days{    11169}});
+        static_assert(sys_days{  2000y/ 8/ 1} == sys_days{days{    11170}});
+        static_assert(sys_days{  2000y/ 8/31} == sys_days{days{    11200}});
+        static_assert(sys_days{  2000y/ 9/ 1} == sys_days{days{    11201}});
+        static_assert(sys_days{  2000y/ 9/30} == sys_days{days{    11230}});
+        static_assert(sys_days{  2000y/10/ 1} == sys_days{days{    11231}});
+        static_assert(sys_days{  2000y/10/31} == sys_days{days{    11261}});
+        static_assert(sys_days{  2000y/11/ 1} == sys_days{days{    11262}});
+        static_assert(sys_days{  2000y/11/30} == sys_days{days{    11291}});
+        static_assert(sys_days{  2000y/12/ 1} == sys_days{days{    11292}});
+        static_assert(sys_days{  2000y/12/31} == sys_days{days{    11322}});
+        static_assert(sys_days{  -400y/ 2/29} == sys_days{days{  -865566}});
+        static_assert(sys_days{  -400y/ 3/ 1} == sys_days{days{  -865565}});
+        static_assert(sys_days{    -1y/ 2/28} == sys_days{days{  -719835}});
+        static_assert(sys_days{    -1y/ 3/ 1} == sys_days{days{  -719834}});
+        static_assert(sys_days{    -1y/12/31} == sys_days{days{  -719529}});
+        static_assert(sys_days{     0y/ 1/ 1} == sys_days{days{  -719528}});
+        static_assert(sys_days{     0y/ 2/29} == sys_days{days{  -719469}});
+        static_assert(sys_days{     0y/ 3/ 1} == sys_days{days{  -719468}});
+        static_assert(sys_days{  1900y/ 3/ 1} == sys_days{days{   -25508}});
+        static_assert(sys_days{  1901y/ 2/28} == sys_days{days{   -25144}});
+        static_assert(sys_days{  1903y/ 3/ 1} == sys_days{days{   -24413}});
+        static_assert(sys_days{  1904y/ 2/29} == sys_days{days{   -24048}});
+        static_assert(sys_days{  1996y/ 3/ 1} == sys_days{days{     9556}});
+        static_assert(sys_days{  1997y/ 2/28} == sys_days{days{     9920}});
+        static_assert(sys_days{  1999y/ 3/ 1} == sys_days{days{    10651}});
+        static_assert(sys_days{  2000y/ 2/29} == sys_days{days{    11016}});
+        static_assert(sys_days{  2000y/ 3/ 1} == sys_days{days{    11017}});
+        static_assert(sys_days{  2001y/ 2/28} == sys_days{days{    11381}});
+        static_assert(sys_days{  2003y/ 3/ 1} == sys_days{days{    12112}});
+        static_assert(sys_days{  2004y/ 2/29} == sys_days{days{    12477}});
+        static_assert(sys_days{  2096y/ 3/ 1} == sys_days{days{    46081}});
+        static_assert(sys_days{  2097y/ 2/28} == sys_days{days{    46445}});
+        static_assert(sys_days{  2099y/ 3/ 1} == sys_days{days{    47176}});
+        static_assert(sys_days{  2100y/ 2/28} == sys_days{days{    47540}});
+        static_assert(sys_days{-32767y/ 1/ 1} == sys_days{days{-12687428}});
+        static_assert(sys_days{ 32767y/12/31} == sys_days{days{ 11248737}});
+
+        static_assert(  2000y/ 1/ 1 == year_month_day{sys_days{days{    10957}}});
+        static_assert(  2000y/ 1/31 == year_month_day{sys_days{days{    10987}}});
+        static_assert(  2000y/ 2/ 1 == year_month_day{sys_days{days{    10988}}});
+        static_assert(  2000y/ 2/29 == year_month_day{sys_days{days{    11016}}});
+        static_assert(  2000y/ 3/ 1 == year_month_day{sys_days{days{    11017}}});
+        static_assert(  2000y/ 3/31 == year_month_day{sys_days{days{    11047}}});
+        static_assert(  2000y/ 4/ 1 == year_month_day{sys_days{days{    11048}}});
+        static_assert(  2000y/ 4/30 == year_month_day{sys_days{days{    11077}}});
+        static_assert(  2000y/ 5/ 1 == year_month_day{sys_days{days{    11078}}});
+        static_assert(  2000y/ 5/31 == year_month_day{sys_days{days{    11108}}});
+        static_assert(  2000y/ 6/ 1 == year_month_day{sys_days{days{    11109}}});
+        static_assert(  2000y/ 6/30 == year_month_day{sys_days{days{    11138}}});
+        static_assert(  2000y/ 7/ 1 == year_month_day{sys_days{days{    11139}}});
+        static_assert(  2000y/ 7/31 == year_month_day{sys_days{days{    11169}}});
+        static_assert(  2000y/ 8/ 1 == year_month_day{sys_days{days{    11170}}});
+        static_assert(  2000y/ 8/31 == year_month_day{sys_days{days{    11200}}});
+        static_assert(  2000y/ 9/ 1 == year_month_day{sys_days{days{    11201}}});
+        static_assert(  2000y/ 9/30 == year_month_day{sys_days{days{    11230}}});
+        static_assert(  2000y/10/ 1 == year_month_day{sys_days{days{    11231}}});
+        static_assert(  2000y/10/31 == year_month_day{sys_days{days{    11261}}});
+        static_assert(  2000y/11/ 1 == year_month_day{sys_days{days{    11262}}});
+        static_assert(  2000y/11/30 == year_month_day{sys_days{days{    11291}}});
+        static_assert(  2000y/12/ 1 == year_month_day{sys_days{days{    11292}}});
+        static_assert(  2000y/12/31 == year_month_day{sys_days{days{    11322}}});
+        static_assert(  -400y/ 2/29 == year_month_day{sys_days{days{  -865566}}});
+        static_assert(  -400y/ 3/ 1 == year_month_day{sys_days{days{  -865565}}});
+        static_assert(    -1y/ 2/28 == year_month_day{sys_days{days{  -719835}}});
+        static_assert(    -1y/ 3/ 1 == year_month_day{sys_days{days{  -719834}}});
+        static_assert(    -1y/12/31 == year_month_day{sys_days{days{  -719529}}});
+        static_assert(     0y/ 1/ 1 == year_month_day{sys_days{days{  -719528}}});
+        static_assert(     0y/ 2/29 == year_month_day{sys_days{days{  -719469}}});
+        static_assert(     0y/ 3/ 1 == year_month_day{sys_days{days{  -719468}}});
+        static_assert(  1900y/ 3/ 1 == year_month_day{sys_days{days{   -25508}}});
+        static_assert(  1901y/ 2/28 == year_month_day{sys_days{days{   -25144}}});
+        static_assert(  1903y/ 3/ 1 == year_month_day{sys_days{days{   -24413}}});
+        static_assert(  1904y/ 2/29 == year_month_day{sys_days{days{   -24048}}});
+        static_assert(  1996y/ 3/ 1 == year_month_day{sys_days{days{     9556}}});
+        static_assert(  1997y/ 2/28 == year_month_day{sys_days{days{     9920}}});
+        static_assert(  1999y/ 3/ 1 == year_month_day{sys_days{days{    10651}}});
+        static_assert(  2000y/ 2/29 == year_month_day{sys_days{days{    11016}}});
+        static_assert(  2000y/ 3/ 1 == year_month_day{sys_days{days{    11017}}});
+        static_assert(  2001y/ 2/28 == year_month_day{sys_days{days{    11381}}});
+        static_assert(  2003y/ 3/ 1 == year_month_day{sys_days{days{    12112}}});
+        static_assert(  2004y/ 2/29 == year_month_day{sys_days{days{    12477}}});
+        static_assert(  2096y/ 3/ 1 == year_month_day{sys_days{days{    46081}}});
+        static_assert(  2097y/ 2/28 == year_month_day{sys_days{days{    46445}}});
+        static_assert(  2099y/ 3/ 1 == year_month_day{sys_days{days{    47176}}});
+        static_assert(  2100y/ 2/28 == year_month_day{sys_days{days{    47540}}});
+        static_assert(-32767y/ 1/ 1 == year_month_day{sys_days{days{-12687428}}});
+        static_assert( 32767y/12/31 == year_month_day{sys_days{days{ 11248737}}});
+
+        static_assert(sys_days{  2000y/ 1/  0} == sys_days{days{    10956}});
+        static_assert(sys_days{  2000y/ 1/255} == sys_days{days{    11211}});
+        static_assert(sys_days{  2000y/ 2/  0} == sys_days{days{    10987}});
+        static_assert(sys_days{  2000y/ 2/255} == sys_days{days{    11242}});
+        static_assert(sys_days{  2000y/ 3/  0} == sys_days{days{    11016}});
+        static_assert(sys_days{  2000y/ 3/255} == sys_days{days{    11271}});
+        static_assert(sys_days{  2000y/ 4/  0} == sys_days{days{    11047}});
+        static_assert(sys_days{  2000y/ 4/255} == sys_days{days{    11302}});
+        static_assert(sys_days{  2000y/ 5/  0} == sys_days{days{    11077}});
+        static_assert(sys_days{  2000y/ 5/255} == sys_days{days{    11332}});
+        static_assert(sys_days{  2000y/ 6/  0} == sys_days{days{    11108}});
+        static_assert(sys_days{  2000y/ 6/255} == sys_days{days{    11363}});
+        static_assert(sys_days{  2000y/ 7/  0} == sys_days{days{    11138}});
+        static_assert(sys_days{  2000y/ 7/255} == sys_days{days{    11393}});
+        static_assert(sys_days{  2000y/ 8/  0} == sys_days{days{    11169}});
+        static_assert(sys_days{  2000y/ 8/255} == sys_days{days{    11424}});
+        static_assert(sys_days{  2000y/ 9/  0} == sys_days{days{    11200}});
+        static_assert(sys_days{  2000y/ 9/255} == sys_days{days{    11455}});
+        static_assert(sys_days{  2000y/10/  0} == sys_days{days{    11230}});
+        static_assert(sys_days{  2000y/10/255} == sys_days{days{    11485}});
+        static_assert(sys_days{  2000y/11/  0} == sys_days{days{    11261}});
+        static_assert(sys_days{  2000y/11/255} == sys_days{days{    11516}});
+        static_assert(sys_days{  2000y/12/  0} == sys_days{days{    11291}});
+        static_assert(sys_days{  2000y/12/255} == sys_days{days{    11546}});
+        static_assert(sys_days{  -400y/ 2/255} == sys_days{days{  -865340}});
+        static_assert(sys_days{  -400y/ 3/  0} == sys_days{days{  -865566}});
+        static_assert(sys_days{    -1y/ 2/255} == sys_days{days{  -719608}});
+        static_assert(sys_days{    -1y/ 3/  0} == sys_days{days{  -719835}});
+        static_assert(sys_days{    -1y/12/255} == sys_days{days{  -719305}});
+        static_assert(sys_days{     0y/ 1/  0} == sys_days{days{  -719529}});
+        static_assert(sys_days{     0y/ 2/255} == sys_days{days{  -719243}});
+        static_assert(sys_days{     0y/ 3/  0} == sys_days{days{  -719469}});
+        static_assert(sys_days{  1900y/ 3/  0} == sys_days{days{   -25509}});
+        static_assert(sys_days{  1901y/ 2/255} == sys_days{days{   -24917}});
+        static_assert(sys_days{  1903y/ 3/  0} == sys_days{days{   -24414}});
+        static_assert(sys_days{  1904y/ 2/255} == sys_days{days{   -23822}});
+        static_assert(sys_days{  1996y/ 3/  0} == sys_days{days{     9555}});
+        static_assert(sys_days{  1997y/ 2/255} == sys_days{days{    10147}});
+        static_assert(sys_days{  1999y/ 3/  0} == sys_days{days{    10650}});
+        static_assert(sys_days{  2000y/ 2/255} == sys_days{days{    11242}});
+        static_assert(sys_days{  2000y/ 3/  0} == sys_days{days{    11016}});
+        static_assert(sys_days{  2001y/ 2/255} == sys_days{days{    11608}});
+        static_assert(sys_days{  2003y/ 3/  0} == sys_days{days{    12111}});
+        static_assert(sys_days{  2004y/ 2/255} == sys_days{days{    12703}});
+        static_assert(sys_days{  2096y/ 3/  0} == sys_days{days{    46080}});
+        static_assert(sys_days{  2097y/ 2/255} == sys_days{days{    46672}});
+        static_assert(sys_days{  2099y/ 3/  0} == sys_days{days{    47175}});
+        static_assert(sys_days{  2100y/ 2/255} == sys_days{days{    47767}});
+        static_assert(sys_days{-32767y/ 1/  0} == sys_days{days{-12687429}});
+        static_assert(sys_days{ 32767y/12/255} == sys_days{days{ 11248961}});
+        // clang-format on
+    } else {
+        sys_days sys2{year{y_min} / 1 / 1};
+
+        for (int iy = y_min; iy <= y_max; ++iy) {
+            const year y{iy};
+
+            for (auto um = 1u; um <= 12u; ++um) {
+                const month m{um};
+
+                const year_month_day ymd_first = y / m / 1;
+                assert(sys_days{ymd_first} == sys2);
+                assert(year_month_day{sys2} == ymd_first);
+
+                const year_month_day ymd_min = y / m / 0;
+                assert(sys_days{ymd_min} == sys2 - days{1});
+
+                const year_month_day ymd_max = y / m / 255;
+                assert(sys_days{ymd_max} == sys2 + days{254});
+
+                const year_month_day ymd_last = y / m / last;
+                sys2 += (ymd_last.day() - 1d);
+                assert(sys_days{ymd_last} == sys2);
+                assert(year_month_day{sys2} == ymd_last);
+
+                sys2 += days{1};
+            }
+        }
+    }
 }
 
 constexpr void year_month_day_last_test() {