diff --git a/icu4c/source/i18n/calendar.cpp b/icu4c/source/i18n/calendar.cpp
index 0a02c33f0d85..7595f094e529 100644
--- a/icu4c/source/i18n/calendar.cpp
+++ b/icu4c/source/i18n/calendar.cpp
@@ -696,16 +696,13 @@ static const char gGregorian[] = "gregorian";
 
 Calendar::Calendar(UErrorCode& success)
 :   UObject(),
-fIsTimeSet(false),
-fAreFieldsSet(false),
-fAreAllFieldsSet(false),
-fAreFieldsVirtuallySet(false),
-fNextStamp(kMinimumUserStamp),
-fTime(0),
-fLenient(true),
-fZone(nullptr),
-fRepeatedWallTime(UCAL_WALLTIME_LAST),
-fSkippedWallTime(UCAL_WALLTIME_LAST)
+  fIsTimeSet(false),
+  fAreFieldsSet(false),
+  fAreAllFieldsSet(false),
+  fAreFieldsVirtuallySet(false),
+  fLenient(true),
+  fRepeatedWallTime(UCAL_WALLTIME_LAST),
+  fSkippedWallTime(UCAL_WALLTIME_LAST)
 {
     validLocale[0] = 0;
     actualLocale[0] = 0;
@@ -724,16 +721,13 @@ fSkippedWallTime(UCAL_WALLTIME_LAST)
 
 Calendar::Calendar(TimeZone* zone, const Locale& aLocale, UErrorCode& success)
 :   UObject(),
-fIsTimeSet(false),
-fAreFieldsSet(false),
-fAreAllFieldsSet(false),
-fAreFieldsVirtuallySet(false),
-fNextStamp(kMinimumUserStamp),
-fTime(0),
-fLenient(true),
-fZone(nullptr),
-fRepeatedWallTime(UCAL_WALLTIME_LAST),
-fSkippedWallTime(UCAL_WALLTIME_LAST)
+  fIsTimeSet(false),
+  fAreFieldsSet(false),
+  fAreAllFieldsSet(false),
+  fAreFieldsVirtuallySet(false),
+  fLenient(true),
+  fRepeatedWallTime(UCAL_WALLTIME_LAST),
+  fSkippedWallTime(UCAL_WALLTIME_LAST)
 {
     validLocale[0] = 0;
     actualLocale[0] = 0;
@@ -759,16 +753,13 @@ fSkippedWallTime(UCAL_WALLTIME_LAST)
 
 Calendar::Calendar(const TimeZone& zone, const Locale& aLocale, UErrorCode& success)
 :   UObject(),
-fIsTimeSet(false),
-fAreFieldsSet(false),
-fAreAllFieldsSet(false),
-fAreFieldsVirtuallySet(false),
-fNextStamp(kMinimumUserStamp),
-fTime(0),
-fLenient(true),
-fZone(nullptr),
-fRepeatedWallTime(UCAL_WALLTIME_LAST),
-fSkippedWallTime(UCAL_WALLTIME_LAST)
+  fIsTimeSet(false),
+  fAreFieldsSet(false),
+  fAreAllFieldsSet(false),
+  fAreFieldsVirtuallySet(false),
+  fLenient(true),
+  fRepeatedWallTime(UCAL_WALLTIME_LAST),
+  fSkippedWallTime(UCAL_WALLTIME_LAST)
 {
     validLocale[0] = 0;
     actualLocale[0] = 0;
@@ -795,7 +786,6 @@ Calendar::~Calendar()
 Calendar::Calendar(const Calendar &source)
 :   UObject(source)
 {
-    fZone = nullptr;
     *this = source;
 }
 
@@ -4229,7 +4219,7 @@ Calendar::recalculateStamp() {
     int32_t currentValue;
     int32_t j, i;
 
-    fNextStamp = 1;
+    fNextStamp = kInternallySet;
 
     for (j = 0; j < UCAL_FIELD_COUNT; j++) {
         currentValue = STAMP_MAX;
diff --git a/icu4c/source/i18n/unicode/calendar.h b/icu4c/source/i18n/unicode/calendar.h
index 8a07c37b8925..5f688ab881fa 100644
--- a/icu4c/source/i18n/unicode/calendar.h
+++ b/icu4c/source/i18n/unicode/calendar.h
@@ -1881,38 +1881,6 @@ class U_I18N_API Calendar : public UObject {
      */
     int32_t getActualHelper(UCalendarDateFields field, int32_t startValue, int32_t endValue, UErrorCode &status) const;
 
-
-private:
-    /**
-     * The flag which indicates if the current time is set in the calendar.
-     */
-    UBool      fIsTimeSet;
-
-    /**
-     * True if the fields are in sync with the currently set time of this Calendar.
-     * If false, then the next attempt to get the value of a field will
-     * force a recomputation of all fields from the current value of the time
-     * field.
-     * <P>
-     * This should really be named areFieldsInSync, but the old name is retained
-     * for backward compatibility.
-     */
-    UBool      fAreFieldsSet;
-
-    /**
-     * True if all of the fields have been set.  This is initially false, and set to
-     * true by computeFields().
-     */
-    UBool      fAreAllFieldsSet;
-
-    /**
-     * True if all fields have been virtually set, but have not yet been
-     * computed.  This occurs only in setTimeInMillis().  A calendar set
-     * to this state will compute all fields from the time if it becomes
-     * necessary, but otherwise will delay such computation.
-     */
-    UBool fAreFieldsVirtuallySet;
-
 protected:
     /**
      * Get the current time without recomputing.
@@ -2169,7 +2137,7 @@ class U_I18N_API Calendar : public UObject {
     /**
      * The next available value for fStamp[]
      */
-    int8_t fNextStamp;// = MINIMUM_USER_STAMP;
+    int8_t fNextStamp = kMinimumUserStamp;
 
     /**
      * Recalculates the time stamp array (fStamp).
@@ -2180,30 +2148,60 @@ class U_I18N_API Calendar : public UObject {
     /**
      * The current time set for the calendar.
      */
-    UDate        fTime;
+    UDate        fTime = 0;
 
     /**
-     * @see   #setLenient
+     * Time zone affects the time calculation done by Calendar. Calendar subclasses use
+     * the time zone data to produce the local time. Always set; never nullptr.
      */
-    UBool      fLenient;
+    TimeZone*   fZone = nullptr;
 
     /**
-     * Time zone affects the time calculation done by Calendar. Calendar subclasses use
-     * the time zone data to produce the local time. Always set; never nullptr.
+     * The flag which indicates if the current time is set in the calendar.
+     */
+    bool      fIsTimeSet:1;
+
+    /**
+     * True if the fields are in sync with the currently set time of this Calendar.
+     * If false, then the next attempt to get the value of a field will
+     * force a recomputation of all fields from the current value of the time
+     * field.
+     * <P>
+     * This should really be named areFieldsInSync, but the old name is retained
+     * for backward compatibility.
+     */
+    bool      fAreFieldsSet:1;
+
+    /**
+     * True if all of the fields have been set.  This is initially false, and set to
+     * true by computeFields().
+     */
+    bool      fAreAllFieldsSet:1;
+
+    /**
+     * True if all fields have been virtually set, but have not yet been
+     * computed.  This occurs only in setTimeInMillis().  A calendar set
+     * to this state will compute all fields from the time if it becomes
+     * necessary, but otherwise will delay such computation.
+     */
+    bool      fAreFieldsVirtuallySet:1;
+
+    /**
+     * @see   #setLenient
      */
-    TimeZone*   fZone;
+    bool      fLenient:1;
 
     /**
      * Option for repeated wall time
      * @see #setRepeatedWallTimeOption
      */
-    UCalendarWallTimeOption fRepeatedWallTime;
+    UCalendarWallTimeOption fRepeatedWallTime:2;
 
     /**
      * Option for skipped wall time
      * @see #setSkippedWallTimeOption
      */
-    UCalendarWallTimeOption fSkippedWallTime;
+    UCalendarWallTimeOption fSkippedWallTime:2;
 
     /**
      * Both firstDayOfWeek and minimalDaysInFirstWeek are locale-dependent. They are
@@ -2213,11 +2211,11 @@ class U_I18N_API Calendar : public UObject {
      * out the week count for a specific date for a given locale. These must be set when
      * a Calendar is constructed.
      */
-    UCalendarDaysOfWeek fFirstDayOfWeek;
+    UCalendarDaysOfWeek fFirstDayOfWeek:3;
+    UCalendarDaysOfWeek fWeekendOnset:3;
+    UCalendarDaysOfWeek fWeekendCease:3;
     uint8_t     fMinimalDaysInFirstWeek;
-    UCalendarDaysOfWeek fWeekendOnset;
     int32_t fWeekendOnsetMillis;
-    UCalendarDaysOfWeek fWeekendCease;
     int32_t fWeekendCeaseMillis;
 
     /**