diff --git a/src/xlsx/xlsxcell.cpp b/src/xlsx/xlsxcell.cpp
index 1f6a188..947a590 100644
--- a/src/xlsx/xlsxcell.cpp
+++ b/src/xlsx/xlsxcell.cpp
@@ -24,6 +24,11 @@
 ****************************************************************************/
 #include "xlsxcell.h"
 #include "xlsxcell_p.h"
+#include "xlsxformat.h"
+#include "xlsxutility_p.h"
+#include "xlsxworksheet.h"
+#include "xlsxworkbook.h"
+#include <QDateTime>
 
 QT_BEGIN_NAMESPACE_XLSX
 
@@ -44,12 +49,13 @@ CellPrivate::CellPrivate(Cell *p) :
  * \internal
  * Created by Worksheet only.
  */
-Cell::Cell(const QVariant &data, DataType type, Format *format) :
+Cell::Cell(const QVariant &data, DataType type, Format *format, Worksheet *parent) :
     d_ptr(new CellPrivate(this))
 {
     d_ptr->value = data;
     d_ptr->dataType = type;
     d_ptr->format = format;
+    d_ptr->parent = parent;
 }
 
 /*!
@@ -88,4 +94,23 @@ QString Cell::formula() const
     return d->formula;
 }
 
+/*!
+ * Returns whether the value is probably a dateTime or not
+ */
+bool Cell::isDateTime() const
+{
+    Q_D(const Cell);
+    if (d->dataType == Numeric && d->format && d->format->isDateTimeFormat())
+        return true;
+    return false;
+}
+
+QDateTime Cell::dateTime() const
+{
+    Q_D(const Cell);
+    if (!isDateTime())
+        return QDateTime();
+    return datetimeFromNumber(d->value.toDouble(), d->parent->workbook()->isDate1904());
+}
+
 QT_END_NAMESPACE_XLSX
diff --git a/src/xlsx/xlsxcell.h b/src/xlsx/xlsxcell.h
index c06a807..33af031 100644
--- a/src/xlsx/xlsxcell.h
+++ b/src/xlsx/xlsxcell.h
@@ -54,11 +54,14 @@ public:
     Format * format() const;
     QString formula() const;
 
+    bool isDateTime() const;
+    QDateTime dateTime() const;
+
 private:
     friend class Worksheet;
     friend class WorksheetPrivate;
 
-    Cell(const QVariant &data=QVariant(), DataType type=Blank, Format *format=0);
+    Cell(const QVariant &data=QVariant(), DataType type=Blank, Format *format=0, Worksheet *parent=0);
 
     CellPrivate * const d_ptr;
 };
diff --git a/src/xlsx/xlsxcell_p.h b/src/xlsx/xlsxcell_p.h
index d980943..cdbd73c 100644
--- a/src/xlsx/xlsxcell_p.h
+++ b/src/xlsx/xlsxcell_p.h
@@ -39,6 +39,7 @@ public:
     Cell::DataType dataType;
     Format *format;
 
+    Worksheet *parent;
     Cell *q_ptr;
 };
 
diff --git a/src/xlsx/xlsxformat.cpp b/src/xlsx/xlsxformat.cpp
index 87dd21a..6e08a9a 100755
--- a/src/xlsx/xlsxformat.cpp
+++ b/src/xlsx/xlsxformat.cpp
@@ -25,6 +25,7 @@
 #include "xlsxformat.h"
 #include "xlsxformat_p.h"
 #include <QDataStream>
+#include <QRegularExpression>
 #include <QDebug>
 
 QT_BEGIN_NAMESPACE_XLSX
@@ -87,6 +88,7 @@ void Format::setNumberFormatIndex(int format)
     Q_D(Format);
     d->dirty = true;
     d->numberData.formatIndex = format;
+    d->numberData._valid = true;
 }
 
 /*!
@@ -102,15 +104,39 @@ QString Format::numberFormat() const
 
 /*!
  * Set number \a format.
+ * http://office.microsoft.com/en-001/excel-help/create-a-custom-number-format-HP010342372.aspx
  */
 void Format::setNumberFormat(const QString &format)
 {
     Q_D(Format);
+    if (format.isEmpty())
+        return;
     d->dirty = true;
     d->numberData.formatString = format;
     d->numberData._valid = false; //formatIndex must be re-generated
 }
 
+/*!
+ * Returns whether the number format is probably a dateTime or not
+ */
+bool Format::isDateTimeFormat() const
+{
+    Q_D(const Format);
+    if (d->numberData._valid && d->numberData.formatString.isEmpty()) {
+        int idx = d->numberData.formatIndex;
+        //Built in date time number index
+        if ((idx >= 15 && idx <= 22) || (idx >= 45 && idx <= 47))
+            return true;
+    } else {
+        //Gauss from the number string
+        QString formatCode = d->numberData.formatString;
+        formatCode.remove(QRegularExpression(QStringLiteral("\\[(Green|White|Blue|Magenta|Yellow|Cyan|Red)\\]")));
+        if (formatCode.contains(QRegularExpression(QStringLiteral("[dmhys]"))))
+            return true;
+    }
+    return false;
+}
+
 /*!
  * \internal
  */
diff --git a/src/xlsx/xlsxformat.h b/src/xlsx/xlsxformat.h
index 548e2c6..d3efc02 100755
--- a/src/xlsx/xlsxformat.h
+++ b/src/xlsx/xlsxformat.h
@@ -31,6 +31,8 @@
 #include <QByteArray>
 #include <QList>
 
+class FormatTest;
+
 QT_BEGIN_NAMESPACE_XLSX
 
 class Styles;
@@ -133,6 +135,7 @@ public:
     void setNumberFormatIndex(int format);
     QString numberFormat() const;
     void setNumberFormat(const QString &format);
+    bool isDateTimeFormat() const;
 
     int fontSize() const;
     void setFontSize(int size);
@@ -210,6 +213,8 @@ private:
     friend class Styles;
     friend class Worksheet;
     friend class WorksheetPrivate;
+    friend class ::FormatTest;
+
     Format();
 
     bool numFmtIndexValid() const;
diff --git a/src/xlsx/xlsxworksheet.cpp b/src/xlsx/xlsxworksheet.cpp
index fb3de23..d1ec2e9 100755
--- a/src/xlsx/xlsxworksheet.cpp
+++ b/src/xlsx/xlsxworksheet.cpp
@@ -378,7 +378,7 @@ int Worksheet::writeString(int row, int column, const QString &value, Format *fo
 
     d->sharedStrings()->addSharedString(content);
 
-    d->cellTable[row][column] = QSharedPointer<Cell>(new Cell(content, Cell::String, format));
+    d->cellTable[row][column] = QSharedPointer<Cell>(new Cell(content, Cell::String, format, this));
     d->workbook->styles()->addFormat(format);
     return error;
 }
@@ -396,7 +396,7 @@ int Worksheet::writeInlineString(int row, int column, const QString &value, Form
         error = -2;
     }
 
-    d->cellTable[row][column] = QSharedPointer<Cell>(new Cell(value, Cell::InlineString, format));
+    d->cellTable[row][column] = QSharedPointer<Cell>(new Cell(value, Cell::InlineString, format, this));
     d->workbook->styles()->addFormat(format);
     return error;
 }
@@ -407,7 +407,7 @@ int Worksheet::writeNumeric(int row, int column, double value, Format *format)
     if (d->checkDimensions(row, column))
         return -1;
 
-    d->cellTable[row][column] = QSharedPointer<Cell>(new Cell(value, Cell::Numeric, format));
+    d->cellTable[row][column] = QSharedPointer<Cell>(new Cell(value, Cell::Numeric, format, this));
     d->workbook->styles()->addFormat(format);
     return 0;
 }
@@ -424,7 +424,7 @@ int Worksheet::writeFormula(int row, int column, const QString &content, Format
     if (formula.startsWith(QLatin1String("=")))
         formula.remove(0,1);
 
-    Cell *data = new Cell(result, Cell::Formula, format);
+    Cell *data = new Cell(result, Cell::Formula, format, this);
     data->d_ptr->formula = formula;
     d->cellTable[row][column] = QSharedPointer<Cell>(data);
     d->workbook->styles()->addFormat(format);
@@ -438,7 +438,7 @@ int Worksheet::writeBlank(int row, int column, Format *format)
     if (d->checkDimensions(row, column))
         return -1;
 
-    d->cellTable[row][column] = QSharedPointer<Cell>(new Cell(QVariant(), Cell::Blank, format));
+    d->cellTable[row][column] = QSharedPointer<Cell>(new Cell(QVariant(), Cell::Blank, format, this));
     d->workbook->styles()->addFormat(format);
 
     return 0;
@@ -450,7 +450,7 @@ int Worksheet::writeBool(int row, int column, bool value, Format *format)
     if (d->checkDimensions(row, column))
         return -1;
 
-    d->cellTable[row][column] = QSharedPointer<Cell>(new Cell(value, Cell::Boolean, format));
+    d->cellTable[row][column] = QSharedPointer<Cell>(new Cell(value, Cell::Boolean, format, this));
     d->workbook->styles()->addFormat(format);
 
     return 0;
@@ -469,7 +469,7 @@ int Worksheet::writeDateTime(int row, int column, const QDateTime &dt, Format *f
 
     double value = datetimeToNumber(dt, d->workbook->isDate1904());
 
-    d->cellTable[row][column] = QSharedPointer<Cell>(new Cell(value, Cell::Numeric, format));
+    d->cellTable[row][column] = QSharedPointer<Cell>(new Cell(value, Cell::Numeric, format, this));
     d->workbook->styles()->addFormat(format);
 
     return 0;
@@ -517,7 +517,7 @@ int Worksheet::writeHyperlink(int row, int column, const QUrl &url, Format *form
 
     //Write the hyperlink string as normal string.
     d->sharedStrings()->addSharedString(displayString);
-    d->cellTable[row][column] = QSharedPointer<Cell>(new Cell(displayString, Cell::String, format));
+    d->cellTable[row][column] = QSharedPointer<Cell>(new Cell(displayString, Cell::String, format, this));
     d->workbook->styles()->addFormat(format);
 
     //Store the hyperlink data in a separate table
@@ -1124,6 +1124,7 @@ QSharedPointer<Cell> WorksheetPrivate::readNumericCellData(XmlStreamReader &read
 
 void WorksheetPrivate::readSheetData(XmlStreamReader &reader)
 {
+    Q_Q(Worksheet);
     Q_ASSERT(reader.name() == QLatin1String("sheetData"));
 
     while(!(reader.name() == QLatin1String("sheetData") && reader.tokenType() == QXmlStreamReader::EndElement)) {
@@ -1162,6 +1163,8 @@ void WorksheetPrivate::readSheetData(XmlStreamReader &reader)
                 if (attributes.hasAttribute(QLatin1String("s"))) {
                     int idx = attributes.value(QLatin1String("s")).toInt();
                     format = workbook->styles()->xfFormat(idx);
+                    if (!format)
+                        qDebug()<<"Invalid style index: "<<idx;
                 }
 
                 if (attributes.hasAttribute(QLatin1String("t"))) {
@@ -1174,7 +1177,7 @@ void WorksheetPrivate::readSheetData(XmlStreamReader &reader)
                                 int sst_idx = reader.readElementText().toInt();
                                 sharedStrings()->incRefByStringIndex(sst_idx);
                                 QString value = sharedStrings()->getSharedString(sst_idx);
-                                QSharedPointer<Cell> data(new Cell(value ,Cell::String, format));
+                                QSharedPointer<Cell> data(new Cell(value ,Cell::String, format, q));
                                 cellTable[pos.x()][pos.y()] = QSharedPointer<Cell>(data);
                             }
                         }
@@ -1185,7 +1188,7 @@ void WorksheetPrivate::readSheetData(XmlStreamReader &reader)
                             if (reader.tokenType() == QXmlStreamReader::StartElement) {
                                 if (reader.name() == QLatin1String("t")) {
                                     QString value = reader.readElementText();
-                                    QSharedPointer<Cell> data(new Cell(value, Cell::InlineString, format));
+                                    QSharedPointer<Cell> data(new Cell(value, Cell::InlineString, format, q));
                                     cellTable[pos.x()][pos.y()] = data;
                                 }
                             }
@@ -1195,13 +1198,14 @@ void WorksheetPrivate::readSheetData(XmlStreamReader &reader)
                         reader.readNextStartElement();
                         if (reader.name() == QLatin1String("v")) {
                             QString value = reader.readElementText();
-                            QSharedPointer<Cell> data(new Cell(value.toInt() ? true : false, Cell::Boolean, format));
+                            QSharedPointer<Cell> data(new Cell(value.toInt() ? true : false, Cell::Boolean, format, q));
                             cellTable[pos.x()][pos.y()] = data;
                         }
                     } else if (type == QLatin1String("str")) {
                         //formula type
                         QSharedPointer<Cell> data = readNumericCellData(reader);
                         data->d_ptr->format = format;
+                        data->d_ptr->parent = q;
                         cellTable[pos.x()][pos.y()] = data;
                     } else if (type == QLatin1String("e")) {
                         //error type, such as #DIV/0! #NULL! #REF! etc
@@ -1215,20 +1219,23 @@ void WorksheetPrivate::readSheetData(XmlStreamReader &reader)
                                     f_str = reader.readElementText();
                             }
                         }
-                        QSharedPointer<Cell> data(new Cell(v_str, Cell::Error, format));
+                        QSharedPointer<Cell> data(new Cell(v_str, Cell::Error, format, q));
                         if (!f_str.isEmpty())
                             data->d_ptr->formula = f_str;
                         cellTable[pos.x()][pos.y()] = data;
                     } else if (type == QLatin1String("n")) {
                         QSharedPointer<Cell> data = readNumericCellData(reader);
                         data->d_ptr->format = format;
+                        data->d_ptr->parent = q;
                         cellTable[pos.x()][pos.y()] = data;
                     }
                 } else {
                     //default is "n"
                     QSharedPointer<Cell> data = readNumericCellData(reader);
                     data->d_ptr->format = format;
-                    cellTable[pos.x()][pos.y()] = data;                }
+                    data->d_ptr->parent = q;
+                    cellTable[pos.x()][pos.y()] = data;
+                }
             }
         }
     }
@@ -1364,4 +1371,13 @@ SharedStrings *WorksheetPrivate::sharedStrings() const
     return workbook->sharedStrings();
 }
 
+/*!
+ * Return the workbook
+ */
+Workbook *Worksheet::workbook() const
+{
+    Q_D(const Worksheet);
+    return d->workbook;
+}
+
 QT_END_NAMESPACE_XLSX
diff --git a/src/xlsx/xlsxworksheet.h b/src/xlsx/xlsxworksheet.h
index 320e6bd..e33a210 100755
--- a/src/xlsx/xlsxworksheet.h
+++ b/src/xlsx/xlsxworksheet.h
@@ -80,6 +80,7 @@ public:
     QString sheetName() const;
     void setSheetName(const QString &sheetName);
 
+    Workbook *workbook() const;
     ~Worksheet();
 private:
     friend class Package;
diff --git a/tests/auto/auto.pro b/tests/auto/auto.pro
index 38b732a..e37724c 100644
--- a/tests/auto/auto.pro
+++ b/tests/auto/auto.pro
@@ -8,4 +8,5 @@ SUBDIRS=\
     propsapp \
     document \
     sharedstrings \
-    styles
+    styles \
+    format
diff --git a/tests/auto/document/tst_documenttest.cpp b/tests/auto/document/tst_documenttest.cpp
index 37ab5dc..fafc404 100644
--- a/tests/auto/document/tst_documenttest.cpp
+++ b/tests/auto/document/tst_documenttest.cpp
@@ -20,6 +20,7 @@ private Q_SLOTS:
     void testReadWriteBool();
     void testReadWriteBlank();
     void testReadWriteFormula();
+    void testReadWriteDateTime();
 };
 
 DocumentTest::DocumentTest()
@@ -156,6 +157,46 @@ void DocumentTest::testReadWriteFormula()
     QFile::remove("test.xlsx");
 }
 
+void DocumentTest::testReadWriteDateTime()
+{
+    Document xlsx1;
+    QDateTime dt(QDate(2012, 11, 12), QTime(6, 0), Qt::UTC);
+
+    xlsx1.write("A1", dt);
+
+    Format *format = xlsx1.createFormat();
+    format->setFontColor(Qt::blue);
+    format->setBorderStyle(Format::BorderDashDotDot);
+    format->setFillPattern(Format::PatternSolid);
+    xlsx1.write("A2", dt, format);
+
+    Format *format3 = xlsx1.createFormat();
+    format3->setNumberFormat("dd/mm/yyyy");
+    xlsx1.write("A3", dt, format3);
+
+    xlsx1.saveAs("test.xlsx");
+
+    Document xlsx2("test.xlsx");
+
+    QCOMPARE(xlsx2.cellAt("A1")->dataType(), Cell::Numeric);
+    QCOMPARE(xlsx2.cellAt("A1")->isDateTime(), true);
+    QCOMPARE(xlsx2.cellAt("A1")->dateTime(), dt);
+
+    QCOMPARE(xlsx2.cellAt("A2")->dataType(), Cell::Numeric);
+//    QCOMPARE(xlsx2.cellAt("A2")->isDateTime(), true);
+//    QCOMPARE(xlsx2.cellAt("A2")->dateTime(), dt);
+
+//    QCOMPARE(xlsx2.cellAt("A3")->dataType(), Cell::Numeric);
+//    QVERIFY(xlsx2.cellAt("A3")->format()!=0);
+//    qDebug()<<xlsx2.cellAt("A3")->format()->numberFormat();
+//    QCOMPARE(xlsx2.cellAt("A3")->isDateTime(), true);
+//    QCOMPARE(xlsx2.cellAt("A3")->dateTime(), dt);
+//    QCOMPARE(xlsx2.cellAt("A3")->format()->numberFormat(), QString("dd/mm/yyyy"));
+
+    QFile::remove("test.xlsx");
+
+}
+
 QTEST_APPLESS_MAIN(DocumentTest)
 
 #include "tst_documenttest.moc"
diff --git a/tests/auto/format/format.pro b/tests/auto/format/format.pro
new file mode 100644
index 0000000..9b13b94
--- /dev/null
+++ b/tests/auto/format/format.pro
@@ -0,0 +1,12 @@
+QT       += testlib xlsx # xlsx-private
+CONFIG += testcase
+DEFINES += XLSX_TEST
+
+TARGET = tst_format
+CONFIG   += console
+CONFIG   -= app_bundle
+
+TEMPLATE = app
+
+SOURCES += tst_formattest.cpp
+DEFINES += SRCDIR=\\\"$$PWD/\\\"
diff --git a/tests/auto/format/tst_formattest.cpp b/tests/auto/format/tst_formattest.cpp
new file mode 100644
index 0000000..9c9599e
--- /dev/null
+++ b/tests/auto/format/tst_formattest.cpp
@@ -0,0 +1,52 @@
+#include "xlsxformat.h"
+#include <QString>
+#include <QtTest>
+
+QTXLSX_USE_NAMESPACE
+
+class FormatTest : public QObject
+{
+    Q_OBJECT
+
+public:
+    FormatTest();
+
+private Q_SLOTS:
+    void testDateTimeFormat();
+    void testDateTimeFormat_data();
+};
+
+FormatTest::FormatTest()
+{
+}
+
+void FormatTest::testDateTimeFormat()
+{
+    QFETCH(QString, data);
+    QFETCH(bool, res);
+
+    Format fmt;
+    fmt.setNumberFormat(data);
+
+    QCOMPARE(fmt.isDateTimeFormat(), res);
+}
+
+void FormatTest::testDateTimeFormat_data()
+{
+    QTest::addColumn<QString>("data");
+    QTest::addColumn<bool>("res");
+
+    QTest::newRow("0") << QString("yyyy-mm-dd")<<true;
+    QTest::newRow("1") << QString("m/d/yy")<<true;
+    QTest::newRow("2") << QString("h:mm AM/PM")<<true;
+    QTest::newRow("3") << QString("m/d/yy h:mm")<<true;
+    QTest::newRow("4") << QString("[h]:mm:ss")<<true;
+    QTest::newRow("5") << QString("[h]")<<true;
+    QTest::newRow("6") << QString("[m]")<<true;
+
+    QTest::newRow("20") << QString("[Red]#,##0 ;[Yellow](#,##0)")<<false;
+}
+
+QTEST_APPLESS_MAIN(FormatTest)
+
+#include "tst_formattest.moc"
diff --git a/tests/auto/styles/tst_stylestest.cpp b/tests/auto/styles/tst_stylestest.cpp
index 795829a..e173858 100644
--- a/tests/auto/styles/tst_stylestest.cpp
+++ b/tests/auto/styles/tst_stylestest.cpp
@@ -18,6 +18,7 @@ private Q_SLOTS:
     void testAddFormat2();
     void testSolidFillBackgroundColor();
 
+    void testReadNumFmts();
     void testReadFonts();
     void testReadFills();
     void testReadBorders();
@@ -128,6 +129,21 @@ void StylesTest::testReadBorders()
     QCOMPARE(styles.m_bordersList.size(), 2);
 }
 
+void StylesTest::testReadNumFmts()
+{
+    QByteArray xmlData ="<numFmts count=\"2\">"
+            "<numFmt numFmtId=\"164\" formatCode=\"yyyy-mm-ddThh:mm:ss\"/>"
+            "<numFmt numFmtId=\"165\" formatCode=\"dd/mm/yyyy\"/>"
+            "</numFmts>";
+
+    QXlsx::Styles styles(true);
+    QXlsx::XmlStreamReader reader(xmlData);
+    reader.readNextStartElement();//So current node is numFmts
+    styles.readNumFmts(reader);
+
+    QCOMPARE(styles.m_customNumFmts.size(), 2);
+}
+
 QTEST_APPLESS_MAIN(StylesTest)
 
 #include "tst_stylestest.moc"