diff --git a/lib/js/runtime.sx b/lib/js/runtime.sx
index d86a627a..ebd6ccc6 100644
--- a/lib/js/runtime.sx
+++ b/lib/js/runtime.sx
@@ -1062,6 +1062,49 @@
         (js-new-call URIError (js-args (js-string-slice e 10 (len e)))))
       (else e))))
 
+(define
+  js-date-time-value
+  (fn
+    (d)
+    (cond
+      ((or (not (dict? d)) (not (contains? (keys d) "__js_is_date__")))
+        (raise (js-new-call TypeError (js-args "this is not a Date object"))))
+      (else (get d "__date_value__")))))
+
+(define
+  js-date-getter
+  (fn
+    (d field)
+    (let
+      ((ms-raw (js-date-time-value d)))
+      (let
+        ((ms (if (= (type-of ms-raw) "rational") (exact->inexact ms-raw) ms-raw)))
+        (cond
+          ((or (= ms nil) (js-undefined? ms) (not (number? ms)))
+            (js-nan-value))
+          ((js-number-is-nan ms) (js-nan-value))
+          (else
+            (let
+              ((days (floor (/ ms 86400000)))
+                (tod
+                  (let ((m (modulo (js-num-to-int ms) 86400000)))
+                    (if (< m 0) (+ m 86400000) m))))
+              (cond
+                ((= field "ms") (modulo tod 1000))
+                ((= field "seconds") (js-math-trunc (/ (modulo tod 60000) 1000)))
+                ((= field "minutes") (js-math-trunc (/ (modulo tod 3600000) 60000)))
+                ((= field "hours") (js-math-trunc (/ tod 3600000)))
+                ((= field "day")
+                  (let ((dow (modulo (+ days 4) 7)))
+                    (if (< dow 0) (+ dow 7) dow)))
+                (else
+                  (let ((ymd (js-date-days-to-ymd days)))
+                    (cond
+                      ((= field "year") (nth ymd 0))
+                      ((= field "month") (- (nth ymd 1) 1))
+                      ((= field "date") (nth ymd 2))
+                      (else (js-nan-value)))))))))))))
+
 (define
   js-date-from-one
   (fn
@@ -1092,15 +1135,53 @@
   (fn
     (args)
     (let
-      ((year (js-num-to-int (js-to-number (nth args 0))))
-        (month
-         (if (>= (len args) 2) (js-num-to-int (js-to-number (nth args 1))) 0))
-        (day
-         (if (>= (len args) 3) (js-num-to-int (js-to-number (nth args 2))) 1)))
-      (+
-        (* (- year 1970) 31557600000)
-        (* month 2629800000)
-        (* (- day 1) 86400000)))))
+      ((year-raw (js-num-to-int (js-to-number (nth args 0)))))
+      (let
+        ((year (if (and (>= year-raw 0) (<= year-raw 99)) (+ year-raw 1900) year-raw))
+          (month
+           (if (>= (len args) 2) (js-num-to-int (js-to-number (nth args 1))) 0))
+          (day
+           (if (>= (len args) 3) (js-num-to-int (js-to-number (nth args 2))) 1))
+          (hour
+           (if (>= (len args) 4) (js-num-to-int (js-to-number (nth args 3))) 0))
+          (mins
+           (if (>= (len args) 5) (js-num-to-int (js-to-number (nth args 4))) 0))
+          (secs
+           (if (>= (len args) 6) (js-num-to-int (js-to-number (nth args 5))) 0))
+          (ms
+           (if (>= (len args) 7) (js-num-to-int (js-to-number (nth args 6))) 0)))
+        (let
+          ((days (js-date-civil-to-days year (+ month 1) day)))
+          (+
+            (* days 86400000)
+            (* hour 3600000)
+            (* mins 60000)
+            (* secs 1000)
+            ms))))))
+
+(define
+  js-date-civil-to-days
+  (fn
+    (y m d)
+    (let
+      ((y2 (if (<= m 2) (- y 1) y)))
+      (let
+        ((era (if (>= y2 0) (js-math-trunc (/ y2 400)) (js-math-trunc (/ (- y2 399) 400)))))
+        (let
+          ((yoe (- y2 (* era 400))))
+          (let
+            ((doy
+               (+
+                 (js-math-trunc (/ (+ (* 153 (if (> m 2) (- m 3) (+ m 9))) 2) 5))
+                 (- d 1))))
+            (let
+              ((doe
+                 (+
+                   (* yoe 365)
+                   (+
+                     (- (js-math-trunc (/ yoe 4)) (js-math-trunc (/ yoe 100)))
+                     doy))))
+              (+ (* era 146097) (- doe 719468)))))))))
 
 (define
   js-date-format-now
@@ -1150,30 +1231,24 @@
           ((= (len args) 0) 0)
           (else (js-date-from-parts args))))
     :prototype
-      {:getTime (fn () (let ((t (js-this))) (get t "__date_value__")))
-        :valueOf (fn () (let ((t (js-this))) (get t "__date_value__")))
-        :getFullYear
-          (fn ()
-            (let ((t (js-this)))
-              (+ 1970 (js-math-trunc (/ (get t "__date_value__") 31557600000)))))
-        :getUTCFullYear
-          (fn ()
-            (let ((t (js-this)))
-              (+ 1970 (js-math-trunc (/ (get t "__date_value__") 31557600000)))))
-        :getMonth (fn () 0)
-        :getUTCMonth (fn () 0)
-        :getDate (fn () 1)
-        :getUTCDate (fn () 1)
-        :getDay (fn () 0)
-        :getUTCDay (fn () 0)
-        :getHours (fn () 0)
-        :getUTCHours (fn () 0)
-        :getMinutes (fn () 0)
-        :getUTCMinutes (fn () 0)
-        :getSeconds (fn () 0)
-        :getUTCSeconds (fn () 0)
-        :getMilliseconds (fn () 0)
-        :getUTCMilliseconds (fn () 0)
+      {:getTime (fn () (js-date-time-value (js-this)))
+        :valueOf (fn () (js-date-time-value (js-this)))
+        :getFullYear (fn () (js-date-getter (js-this) "year"))
+        :getUTCFullYear (fn () (js-date-getter (js-this) "year"))
+        :getMonth (fn () (js-date-getter (js-this) "month"))
+        :getUTCMonth (fn () (js-date-getter (js-this) "month"))
+        :getDate (fn () (js-date-getter (js-this) "date"))
+        :getUTCDate (fn () (js-date-getter (js-this) "date"))
+        :getDay (fn () (js-date-getter (js-this) "day"))
+        :getUTCDay (fn () (js-date-getter (js-this) "day"))
+        :getHours (fn () (js-date-getter (js-this) "hours"))
+        :getUTCHours (fn () (js-date-getter (js-this) "hours"))
+        :getMinutes (fn () (js-date-getter (js-this) "minutes"))
+        :getUTCMinutes (fn () (js-date-getter (js-this) "minutes"))
+        :getSeconds (fn () (js-date-getter (js-this) "seconds"))
+        :getUTCSeconds (fn () (js-date-getter (js-this) "seconds"))
+        :getMilliseconds (fn () (js-date-getter (js-this) "ms"))
+        :getUTCMilliseconds (fn () (js-date-getter (js-this) "ms"))
         :getTimezoneOffset (fn () 0)
         :setTime
           (fn (v)
@@ -6617,6 +6692,7 @@
   (dict-set! (get Map "prototype") "__proto__" (get Object "prototype"))
   (dict-set! (get Set "prototype") "__proto__" (get Object "prototype"))
   (dict-set! (get Date "prototype") "__proto__" (get Object "prototype"))
+  (dict-set! (get Date "prototype") "constructor" Date)
   (dict-set! (get RegExp "prototype") "__proto__" (get Object "prototype"))
   (dict-set! (get RegExp "prototype") "constructor" RegExp)
   (dict-set! (get js-function-global "prototype") "__proto__" (get Object "prototype"))
diff --git a/plans/js-on-sx.md b/plans/js-on-sx.md
index 8f576757..85649175 100644
--- a/plans/js-on-sx.md
+++ b/plans/js-on-sx.md
@@ -158,6 +158,8 @@ Each item: implement → tests → update progress. Mark `[x]` when tests green.
 
 Append-only record of completed iterations. Loop writes one line per iteration: date, what was done, test count delta.
 
+- 2026-05-10 — **Real `Date` construction + getters via Howard-Hinnant civil-day arithmetic.** `js-date-from-parts` now computes a true ms-since-epoch from `(year, month, day, hour, min, sec, ms)` via `js-date-civil-to-days` (the inverse of last iteration's `days-to-ymd`), with the legacy 2-digit-year coercion (0..99 → 1900+y). `getFullYear/Month/Date/Day/Hours/Minutes/Seconds/Milliseconds` (UTC + non-UTC) all share a new `js-date-getter`: TypeErrors on non-Date this, returns NaN on invalid time, otherwise decomposes ms into y/m/d/h/m/s/ms/dow. Plus added `Date.prototype.constructor = Date` (was missing). Result: each of the 8 Date getter categories went 2/6 → 5/6 (+3 each, +24 total). Date toISOString 11/16 → 13/16. Some Date construction-loop tests now exceed the 15s per-test timeout — the new civil math is heavier than the old (year-1970)*ms-per-year approximation, but correctness wins. conformance.sh: 148/148.
+
 - 2026-05-10 — **`Date.prototype.toISOString` produces real `YYYY-MM-DDTHH:mm:ss.sssZ` and validates input.** Old `js-date-iso` only computed the year and hardcoded the rest as `01-01T00:00:00.000Z`. Added: (1) TypeError when this isn't a Date (no `__js_is_date__` slot); (2) RangeError when ms is NaN, undefined, or |ms| > 8.64e15; (3) full date breakdown via Howard-Hinnant `days_to_civil` algorithm (`js-date-days-to-ymd`) → year/month/day, plus modular hours/min/sec/ms; (4) extended-year format `±YYYYYY` for years outside 0..9999. Result: built-ins/Date/prototype/toISOString 7/16 → 11/16 (+4). Date 21/30. conformance.sh: 148/148.
 
 - 2026-05-10 — **`JSON.stringify` honours `replacer` (function + array forms), `space`, and `toJSON`.** Previous impl ignored the second/third arguments entirely and never called `toJSON`. Rewrote around a `js-json-serialize-property(key, holder, rep-fn, rep-keys, gap, indent)` core: walks `toJSON` first, then replacer-fn (with `holder` as `this`); arrays-as-replacer become a property-name allowlist; numeric `space` clamped to 0..10 spaces, string `space` truncated to 10 chars, non-empty gap activates indented output with `:` → `: ` separator. Number wrapper / String wrapper / Boolean wrapper unwrap before serialization; non-finite numbers serialize as `"null"`; functions serialize as `undefined`. Result: built-ins/JSON/stringify 6/30 → 14/30 (+8). conformance.sh: 148/148.