diff --git a/src/corelib/time/qtimezone.cpp b/src/corelib/time/qtimezone.cpp
index 4976ea5fcb8..c593af544f0 100644
--- a/src/corelib/time/qtimezone.cpp
+++ b/src/corelib/time/qtimezone.cpp
@@ -452,11 +452,13 @@ QTimeZone::Data &QTimeZone::Data::operator=(QTimeZonePrivate *dptr) noexcept
     Creates a time zone instance with the requested IANA ID \a ianaId.
 
     The ID must be one of the available system IDs or a valid UTC-with-offset
-    ID, otherwise an invalid time zone will be returned.
+    ID, otherwise an invalid time zone will be returned. For UTC-with-offset
+    IDs, when they are not in fact IANA IDs, the \c{id()} of the resulting
+    instance may differ from the ID passed to the constructor.
 
     This constructor is only available when feature \c timezone is enabled.
 
-    \sa availableTimeZoneIds()
+    \sa availableTimeZoneIds(), id()
 */
 
 QTimeZone::QTimeZone(const QByteArray &ianaId)
@@ -498,7 +500,7 @@ QTimeZone::QTimeZone(const QByteArray &ianaId)
     \c{QTimeZone::fromSecondsAfterUtc(offsetSeconds)}, albeit implemented as a
     time zone.
 
-    \sa MinUtcOffsetSecs, MaxUtcOffsetSecs
+    \sa MinUtcOffsetSecs, MaxUtcOffsetSecs, id()
 */
 
 QTimeZone::QTimeZone(int offsetSeconds)
@@ -790,6 +792,28 @@ bool QTimeZone::isValid() const
     IANA IDs are used on all platforms.  On Windows these are translated from
     the Windows ID into the best match IANA ID for the time zone and territory.
 
+    If this timezone instance was not constructed from an IANA ID, its ID is
+    determined by how it was constructed. In most cases, the ID passed when
+    constructing the instance is used. (The constructor for a custom zone uses
+    the ID it is passed, which must not be an IANA ID.) There are two
+    exceptions.
+    \list
+    \li Instances constructed by passing only a UTC offset in seconds have no ID
+        passed when constructing.
+    \li The constructor taking only an IANA ID will also accept some UTC-offset
+        IDs that are not in fact IANA IDs: its handling of these is equivalent
+        to passing the corresponding offset in seconds, as for the first
+        exception.
+    \endlist
+
+    In the two exceptional cases, if there is an IANA UTC-offset zone with the
+    specified offset, the instance constructed uses that IANA zone's ID, even
+    though this may differ from the (non-IANA) UTC-offset ID passed to the
+    constructor. Otherwise, the instance uses an ID synthesized from its offset,
+    with the form UTC±hh:mm:ss, omitting any trailing :00 for zero seconds or
+    minutes. Again, this may differ from the UTC-offset ID passed to the
+    constructor.
+
     This method is only available when feature \c timezone is enabled.
 */
 
@@ -1404,6 +1428,9 @@ QTimeZone QTimeZone::utc()
 /*!
     Returns \c true if a given time zone \a ianaId is available on this system.
 
+    This may include some non-IANA IDs, notably UTC-offset IDs, that are not
+    listed in \l availableTimeZoneIds().
+
     This method is only available when feature \c timezone is enabled.
 
     \sa availableTimeZoneIds()
@@ -1441,6 +1468,10 @@ static QList<QByteArray> set_union(const QList<QByteArray> &l1, const QList<QByt
 
     This method is only available when feature \c timezone is enabled.
 
+    \note the QTimeZone constructor will also accept some UTC-offset IDs that
+    are not in the list returned - it would be impractical to list all possible
+    UTC-offset IDs.
+
     \sa isTimeZoneIdAvailable()
 */
 
@@ -1454,7 +1485,7 @@ QList<QByteArray> QTimeZone::availableTimeZoneIds()
     Returns a list of all available IANA time zone IDs for a given \a territory.
 
     As a special case, a \a territory of \l {QLocale::}{AnyTerritory} selects
-    those time zones that have no kown territorial association, such as UTC. If
+    those time zones that have no known territorial association, such as UTC. If
     you require a list of all time zone IDs for all territories then use the
     standard availableTimeZoneIds() method.
 
diff --git a/src/corelib/time/qtimezoneprivate.cpp b/src/corelib/time/qtimezoneprivate.cpp
index d9a14ac36be..97f2f85e52a 100644
--- a/src/corelib/time/qtimezoneprivate.cpp
+++ b/src/corelib/time/qtimezoneprivate.cpp
@@ -813,11 +813,25 @@ qint64 QUtcTimeZonePrivate::offsetFromUtcString(const QByteArray &id)
     return seconds * sign;
 }
 
-// Create offset from UTC
+// Create from UTC offset:
 QUtcTimeZonePrivate::QUtcTimeZonePrivate(qint32 offsetSeconds)
 {
-    QString utcId = isoOffsetFormat(offsetSeconds, QTimeZone::ShortName);
-    init(utcId.toUtf8(), offsetSeconds, utcId, utcId, QLocale::AnyTerritory, utcId);
+    QString name;
+    QByteArray id;
+    // If there's an IANA ID for this offset, use it:
+    const auto data = std::lower_bound(std::begin(utcDataTable), std::end(utcDataTable),
+                                       offsetSeconds, atLowerUtcOffset);
+    if (data != std::end(utcDataTable) && data->offsetFromUtc == offsetSeconds) {
+        QByteArrayView ianaId = data->id();
+        qsizetype cut = ianaId.indexOf(' ');
+        id = (cut < 0 ? ianaId : ianaId.first(cut)).toByteArray();
+        name = QString::fromUtf8(id);
+        Q_ASSERT(!name.isEmpty());
+    } else { // Fall back to a UTC-offset name:
+        name = isoOffsetFormat(offsetSeconds, QTimeZone::ShortName);
+        id = name.toUtf8();
+    }
+    init(id, offsetSeconds, name, name, QLocale::AnyTerritory, name);
 }
 
 QUtcTimeZonePrivate::QUtcTimeZonePrivate(const QByteArray &zoneId, int offsetSeconds,
diff --git a/tests/auto/corelib/time/qdatetime/tst_qdatetime.cpp b/tests/auto/corelib/time/qdatetime/tst_qdatetime.cpp
index c03c7a89e9d..7ae4a8b52e4 100644
--- a/tests/auto/corelib/time/qdatetime/tst_qdatetime.cpp
+++ b/tests/auto/corelib/time/qdatetime/tst_qdatetime.cpp
@@ -4197,7 +4197,7 @@ void tst_QDateTime::timeZones() const
     QCOMPARE(nzStdOffset.date(), QDate(2012, 6, 1));
     QCOMPARE(nzStdOffset.time(), QTime(12, 0));
     QVERIFY(nzStdOffset.timeZone() == nzTzOffset);
-    QCOMPARE(nzStdOffset.timeZone().id(), QByteArray("UTC+12"));
+    QCOMPARE(nzStdOffset.timeZone().id(), QByteArray("UTC+12:00"));
     QCOMPARE(nzStdOffset.offsetFromUtc(), 43200);
     QVERIFY(!nzStdOffset.isDaylightTime());
     QCOMPARE(nzStdOffset.toMSecsSinceEpoch(), utcStd.toMSecsSinceEpoch());
diff --git a/tests/auto/corelib/time/qtimezone/tst_qtimezone.cpp b/tests/auto/corelib/time/qtimezone/tst_qtimezone.cpp
index 29643b2caca..6b0ce704568 100644
--- a/tests/auto/corelib/time/qtimezone/tst_qtimezone.cpp
+++ b/tests/auto/corelib/time/qtimezone/tst_qtimezone.cpp
@@ -537,12 +537,14 @@ void tst_QTimeZone::isTimeZoneIdAvailable()
     for (const QByteArray &id : available) {
         QVERIFY2(QTimeZone::isTimeZoneIdAvailable(id), id);
         QVERIFY2(QTimeZone(id).isValid(), id);
+        QCOMPARE(QTimeZone(id).id(), id);
     }
     for (qint32 offset = QTimeZone::MinUtcOffsetSecs;
          offset <= QTimeZone::MinUtcOffsetSecs; ++offset) {
         const QByteArray id = QTimeZone(offset).id();
         QVERIFY2(QTimeZone::isTimeZoneIdAvailable(id), id);
         QVERIFY2(QTimeZone(id).isValid(), id);
+        QCOMPARE(QTimeZone(id).id(), id);
     }
 }
 
@@ -607,7 +609,11 @@ void tst_QTimeZone::utcOffsetId_data()
     ROW("UTC-11", true, -39600);
     ROW("UTC-09", true, -32400);
     ROW("UTC-08", true, -28800);
+    ROW("UTC-8", true, -28800);
+    ROW("UTC-2:5", true, -7500);
     ROW("UTC-02", true, -7200);
+    ROW("UTC+2", true, 7200);
+    ROW("UTC+2:5", true, 7500);
     ROW("UTC+12", true, 43200);
     ROW("UTC+13", true, 46800);
     // Encountered in bug reports:
@@ -655,6 +661,19 @@ void tst_QTimeZone::utcOffsetId()
         QFETCH(int, offset);
         QCOMPARE(zone.offsetFromUtc(epoch), offset);
         QVERIFY(!zone.hasDaylightTime());
+
+        // zone.id() will be an IANA ID with zero minutes field if original was
+        // a UTC offset by a whole number of hours. It will also zero-pad a
+        // single-digit hour or minute to two digits.
+        if (const qsizetype cut = id.indexOf(':'); cut >= 0) {
+            if (id.size() == cut + 2) // "...:m" -> "...:0m"
+                id.insert(cut + 1, '0');
+        } else if (zone.id().contains(':')) {
+            id += ":00";
+        }
+        if (id.indexOf(':') == 5) // UTC±h:mm -> UTC±0h:mm
+            id.insert(4, '0');
+
         QCOMPARE(zone.id(), id);
     }
 }
@@ -1175,15 +1194,22 @@ void tst_QTimeZone::utcTest()
     QCOMPARE(tzp.hasDaylightTime(), false);
     QCOMPARE(tzp.hasTransitions(), false);
 
-    // Test create from UTC Offset (uses minimal id, skipping minutes if 0)
+    // Test create from UTC Offset:
     QDateTime now = QDateTime::currentDateTime();
     QTimeZone tz(36000);
     QVERIFY(tz.isValid());
-    QCOMPARE(tz.id(), QByteArray("UTC+10"));
+    QCOMPARE(tz.id(), QByteArray("UTC+10:00"));
     QCOMPARE(tz.offsetFromUtc(now), 36000);
     QCOMPARE(tz.standardTimeOffset(now), 36000);
     QCOMPARE(tz.daylightTimeOffset(now), 0);
 
+    tz = QTimeZone(15 * 3600); // no IANA ID, so uses minimal id, skipping :00 minutes
+    QVERIFY(tz.isValid());
+    QCOMPARE(tz.id(), QByteArray("UTC+15"));
+    QCOMPARE(tz.offsetFromUtc(now), 15 * 3600);
+    QCOMPARE(tz.standardTimeOffset(now), 15 * 3600);
+    QCOMPARE(tz.daylightTimeOffset(now), 0);
+
     // Test validity range of UTC offsets:
     int min = QTimeZone::MinUtcOffsetSecs;
     int max = QTimeZone::MaxUtcOffsetSecs;