diff --git a/examples/xlsx/numberformat/main.cpp b/examples/xlsx/numberformat/main.cpp
new file mode 100644
index 0000000..967ceb3
--- /dev/null
+++ b/examples/xlsx/numberformat/main.cpp
@@ -0,0 +1,52 @@
+#include <QtGui>
+#include "xlsxdocument.h"
+#include "xlsxformat.h"
+
+int main(int argc, char** argv)
+{
+    QGuiApplication(argc, argv);
+
+    QXlsx::Document xlsx;
+    xlsx.setColumn(0, 4, 20.0);
+
+    QXlsx::Format *header = xlsx.createFormat();
+    header->setFontBold(true);
+    header->setFontSize(20);
+
+    //Custom number formats
+    QStringList numFormats;
+    numFormats<<"Qt #"
+             <<"yyyy-mmm-dd"
+            <<"$ #,##0.00"
+           <<"[red]0.00";
+    xlsx.write(0, 0, "Raw data", header);
+    xlsx.write(0, 1, "Format", header);
+    xlsx.write(0, 2, "Shown value", header);
+    for (int i=0; i<numFormats.size(); ++i) {
+        int row = i+1;
+        xlsx.write(row, 0, 100.0);
+        xlsx.write(row, 1, numFormats[i]);
+        QXlsx::Format *format = xlsx.createFormat();
+        format->setNumberFormat(numFormats[i]);
+        xlsx.write(row, 2, 100.0, format);
+    }
+
+    //Builtin number formats
+    xlsx.addWorksheet();
+    xlsx.setColumn(0, 4, 20.0);
+    xlsx.write(0, 0, "Raw data", header);
+    xlsx.write(0, 1, "Builtin Format", header);
+    xlsx.write(0, 2, "Shown value", header);
+    for (int i=0; i<50; ++i) {
+        int row = i+1;
+        int numFmt = i;
+        xlsx.write(row, 0, 100.0);
+        xlsx.write(row, 1, numFmt);
+        QXlsx::Format *format = xlsx.createFormat();
+        format->setNumberFormatIndex(numFmt);
+        xlsx.write(row, 2, 100.0, format);
+    }
+
+    xlsx.save();
+    return 0;
+}
diff --git a/examples/xlsx/numberformat/numberformat.pro b/examples/xlsx/numberformat/numberformat.pro
new file mode 100644
index 0000000..eb3863f
--- /dev/null
+++ b/examples/xlsx/numberformat/numberformat.pro
@@ -0,0 +1,12 @@
+TARGET = mergecells
+
+#include(../../../src/xlsx/qtxlsx.pri)
+QT += xlsx
+
+TARGET = numberformat
+CONFIG   += console
+CONFIG   -= app_bundle
+
+TEMPLATE = app
+
+SOURCES += main.cpp
diff --git a/examples/xlsx/style/main.cpp b/examples/xlsx/style/main.cpp
index 7ce890a..ba1bee1 100644
--- a/examples/xlsx/style/main.cpp
+++ b/examples/xlsx/style/main.cpp
@@ -43,7 +43,7 @@ int main()
     xlsx.setColumn(8, 15, 5.0, format4);
 
     QXlsx::Format *format5 = xlsx.createFormat();
-    format5->setNumberFormat(22);
+    format5->setNumberFormatIndex(22);
     xlsx.write("A5", QDate(2013, 8, 29), format5);
 
     QXlsx::Format *format6 = xlsx.createFormat();
diff --git a/examples/xlsx/xlsx.pro b/examples/xlsx/xlsx.pro
index 05c328b..db7d416 100644
--- a/examples/xlsx/xlsx.pro
+++ b/examples/xlsx/xlsx.pro
@@ -3,5 +3,6 @@ SUBDIRS = hello style \
     documentproperty \
     image \
     mergecells \
-    rowcolumn
+    rowcolumn \
+    numberformat
 
diff --git a/src/xlsx/xlsxformat.cpp b/src/xlsx/xlsxformat.cpp
index e19483e..37c9449 100755
--- a/src/xlsx/xlsxformat.cpp
+++ b/src/xlsx/xlsxformat.cpp
@@ -68,19 +68,50 @@ Format::~Format()
     delete d_ptr;
 }
 
-int Format::numberFormat() const
+int Format::numberFormatIndex() const
 {
     Q_D(const Format);
     return d->numberData.formatIndex;
 }
 
-void Format::setNumberFormat(int format)
+void Format::setNumberFormatIndex(int format)
 {
     Q_D(Format);
     d->dirty = true;
     d->numberData.formatIndex = format;
 }
 
+QString Format::numberFormat() const
+{
+    Q_D(const Format);
+    return d->numberData.formatString;
+}
+
+void Format::setNumberFormat(const QString &format)
+{
+    Q_D(Format);
+    d->dirty = true;
+    d->numberData.formatString = format;
+    d->numberData._valid = false; //formatIndex must be re-generated
+}
+
+bool Format::numFmtIndexValid() const
+{
+    Q_D(const Format);
+    return d->numberData._valid;
+}
+
+/*!
+ * \internal
+ */
+void Format::setNumFmt(int index, const QString &string)
+{
+    Q_D(Format);
+    d->numberData.formatIndex = index;
+    d->numberData.formatString = string;
+    d->numberData._valid = true;
+}
+
 int Format::fontSize() const
 {
     Q_D(const Format);
diff --git a/src/xlsx/xlsxformat.h b/src/xlsx/xlsxformat.h
index 948701f..548e2c6 100755
--- a/src/xlsx/xlsxformat.h
+++ b/src/xlsx/xlsxformat.h
@@ -129,8 +129,10 @@ public:
 
     ~Format();
 
-    int numberFormat() const;
-    void setNumberFormat(int format);
+    int numberFormatIndex() const;
+    void setNumberFormatIndex(int format);
+    QString numberFormat() const;
+    void setNumberFormat(const QString &format);
 
     int fontSize() const;
     void setFontSize(int size);
@@ -210,6 +212,9 @@ private:
     friend class WorksheetPrivate;
     Format();
 
+    bool numFmtIndexValid() const;
+    void setNumFmt(int index, const QString &string);
+
     bool fontIndexValid() const;
     int fontIndex() const;
     void setFontIndex(int index);
diff --git a/src/xlsx/xlsxformat_p.h b/src/xlsx/xlsxformat_p.h
index 3adb919..9418a98 100644
--- a/src/xlsx/xlsxformat_p.h
+++ b/src/xlsx/xlsxformat_p.h
@@ -30,9 +30,12 @@ namespace QXlsx {
 
 struct NumberData
 {
-    NumberData() : formatIndex(0) {}
+    NumberData() : formatIndex(0), _valid(true) {}
 
     int formatIndex;
+    QString formatString;
+
+    bool _valid;
 };
 
 struct FontData
diff --git a/src/xlsx/xlsxstyles.cpp b/src/xlsx/xlsxstyles.cpp
index 0c57e88..490ce02 100755
--- a/src/xlsx/xlsxstyles.cpp
+++ b/src/xlsx/xlsxstyles.cpp
@@ -65,6 +65,61 @@ void Styles::addFormat(Format *format)
     if (!format)
         return;
 
+    //numFmt
+    if (!format->numFmtIndexValid()) {
+        if (m_builtinNumFmtsHash.isEmpty()) {
+            m_builtinNumFmtsHash.insert(QStringLiteral("General"), 0);
+            m_builtinNumFmtsHash.insert(QStringLiteral("0"), 1);
+            m_builtinNumFmtsHash.insert(QStringLiteral("0.00"), 2);
+            m_builtinNumFmtsHash.insert(QStringLiteral("#,##0"), 3);
+            m_builtinNumFmtsHash.insert(QStringLiteral("#,##0.00"), 4);
+            m_builtinNumFmtsHash.insert(QStringLiteral("($#,##0_);($#,##0)"), 5);
+            m_builtinNumFmtsHash.insert(QStringLiteral("($#,##0_);[Red]($#,##0)"), 6);
+            m_builtinNumFmtsHash.insert(QStringLiteral("($#,##0.00_);($#,##0.00)"), 7);
+            m_builtinNumFmtsHash.insert(QStringLiteral("($#,##0.00_);[Red]($#,##0.00)"), 8);
+            m_builtinNumFmtsHash.insert(QStringLiteral("0%"), 9);
+            m_builtinNumFmtsHash.insert(QStringLiteral("0.00%"), 10);
+            m_builtinNumFmtsHash.insert(QStringLiteral("0.00E+00"), 11);
+            m_builtinNumFmtsHash.insert(QStringLiteral("# ?/?"), 12);
+            m_builtinNumFmtsHash.insert(QStringLiteral("# ??/??"), 13);
+            m_builtinNumFmtsHash.insert(QStringLiteral("m/d/yy"), 14);
+            m_builtinNumFmtsHash.insert(QStringLiteral("d-mmm-yy"), 15);
+            m_builtinNumFmtsHash.insert(QStringLiteral("d-mmm"), 16);
+            m_builtinNumFmtsHash.insert(QStringLiteral("mmm-yy"), 17);
+            m_builtinNumFmtsHash.insert(QStringLiteral("h:mm AM/PM"), 18);
+            m_builtinNumFmtsHash.insert(QStringLiteral("h:mm:ss AM/PM"), 19);
+            m_builtinNumFmtsHash.insert(QStringLiteral("h:mm"), 20);
+            m_builtinNumFmtsHash.insert(QStringLiteral("h:mm:ss"), 21);
+            m_builtinNumFmtsHash.insert(QStringLiteral("m/d/yy h:mm"), 22);
+
+            m_builtinNumFmtsHash.insert(QStringLiteral("(#,##0_);(#,##0)"), 37);
+            m_builtinNumFmtsHash.insert(QStringLiteral("(#,##0_);[Red](#,##0)"), 38);
+            m_builtinNumFmtsHash.insert(QStringLiteral("(#,##0.00_);(#,##0.00)"), 39);
+            m_builtinNumFmtsHash.insert(QStringLiteral("(#,##0.00_);[Red](#,##0.00)"), 40);
+            m_builtinNumFmtsHash.insert(QStringLiteral("_(* #,##0_);_(* (#,##0);_(* \"-\"_);_(_)"), 41);
+            m_builtinNumFmtsHash.insert(QStringLiteral("_($* #,##0_);_($* (#,##0);_($* \"-\"_);_(_)"), 42);
+            m_builtinNumFmtsHash.insert(QStringLiteral("_(* #,##0.00_);_(* (#,##0.00);_(* \"-\"??_);_(_)"), 43);
+            m_builtinNumFmtsHash.insert(QStringLiteral("_($* #,##0.00_);_($* (#,##0.00);_($* \"-\"??_);_(_)"), 44);
+            m_builtinNumFmtsHash.insert(QStringLiteral("mm:ss"), 45);
+            m_builtinNumFmtsHash.insert(QStringLiteral("[h]:mm:ss"), 46);
+            m_builtinNumFmtsHash.insert(QStringLiteral("mm:ss.0"), 47);
+            m_builtinNumFmtsHash.insert(QStringLiteral("##0.0E+0"), 48);
+            m_builtinNumFmtsHash.insert(QStringLiteral("@"), 49);
+        }
+        const QString str = format->numberFormat();
+        //Assign proper number format index
+        if (m_builtinNumFmtsHash.contains(str)) {
+            format->setNumFmt(m_builtinNumFmtsHash[str], str);
+        } else if (m_customNumFmtsHash.contains(str)) {
+            format->setNumFmt(m_customNumFmtsHash[str], str);
+        } else {
+            int idx = 164 + m_customNumFmts.size();
+            m_customNumFmts.append(str);
+            m_customNumFmtsHash.insert(str, idx);
+            format->setNumFmt(idx, str);
+        }
+    }
+
     //Font
     if (!format->fontIndexValid()) {
         if (!m_fontsHash.contains(format->fontKey())) {
@@ -140,9 +195,7 @@ void Styles::saveToXmlFile(QIODevice *device)
     writer.writeStartElement(QStringLiteral("styleSheet"));
     writer.writeAttribute(QStringLiteral("xmlns"), QStringLiteral("http://schemas.openxmlformats.org/spreadsheetml/2006/main"));
 
-//    writer.writeStartElement(QStringLiteral("numFmts"));
-//    writer.writeEndElement();//numFmts
-
+    writeNumFmts(writer);
     writeFonts(writer);
     writeFills(writer);
     writeBorders(writer);
@@ -180,6 +233,17 @@ void Styles::saveToXmlFile(QIODevice *device)
     writer.writeEndDocument();
 }
 
+void Styles::writeNumFmts(XmlStreamWriter &writer)
+{
+    writer.writeStartElement(QStringLiteral("numFmts"));
+    for (int i=0; i<m_customNumFmts.size(); ++i) {
+        writer.writeEmptyElement(QStringLiteral("numFmt"));
+        writer.writeAttribute(QStringLiteral("numFmtId"), QString::number(164 + i));
+        writer.writeAttribute(QStringLiteral("formatCode"), m_customNumFmts[i]);
+    }
+    writer.writeEndElement();//numFmts
+}
+
 /*
  not consider dxf format.
 */
@@ -394,7 +458,7 @@ void Styles::writeCellXfs(XmlStreamWriter &writer)
     writer.writeStartElement(QStringLiteral("cellXfs"));
     writer.writeAttribute(QStringLiteral("count"), QString::number(m_xf_formatsList.size()));
     foreach (Format *format, m_xf_formatsList) {
-        int num_fmt_id = format->numberFormat();
+        int num_fmt_id = format->numberFormatIndex();
         int font_id = format->fontIndex();
         int fill_id = format->fillIndex();
         int border_id = format->borderIndex();
@@ -405,7 +469,7 @@ void Styles::writeCellXfs(XmlStreamWriter &writer)
         writer.writeAttribute(QStringLiteral("fillId"), QString::number(fill_id));
         writer.writeAttribute(QStringLiteral("borderId"), QString::number(border_id));
         writer.writeAttribute(QStringLiteral("xfId"), QString::number(xf_id));
-        if (format->numberFormat() > 0)
+        if (format->numberFormatIndex() > 0)
             writer.writeAttribute(QStringLiteral("applyNumberFormat"), QStringLiteral("1"));
         if (format->fontIndex() > 0)
             writer.writeAttribute(QStringLiteral("applyFont"), QStringLiteral("1"));
diff --git a/src/xlsx/xlsxstyles_p.h b/src/xlsx/xlsxstyles_p.h
index 49b9d10..91faa67 100755
--- a/src/xlsx/xlsxstyles_p.h
+++ b/src/xlsx/xlsxstyles_p.h
@@ -29,6 +29,7 @@
 #include <QSharedPointer>
 #include <QHash>
 #include <QList>
+#include <QStringList>
 
 class QIODevice;
 
@@ -56,6 +57,7 @@ public:
 private:
     friend class Format;
 
+    void writeNumFmts(XmlStreamWriter &writer);
     void writeFonts(XmlStreamWriter &writer);
     void writeFills(XmlStreamWriter &writer);
     void writeFill(XmlStreamWriter &writer, FillData *fill);
@@ -64,6 +66,9 @@ private:
     void writeCellXfs(XmlStreamWriter &writer);
     void writeDxfs(XmlStreamWriter &writer);
 
+    QHash<QString, int> m_builtinNumFmtsHash;
+    QStringList m_customNumFmts;
+    QHash<QString, int> m_customNumFmtsHash;
     QList<QSharedPointer<FontData> > m_fontsList; //Keep a copy of unique fonts
     QList<QSharedPointer<FillData> > m_fillsList; //Keep a copy of unique fills
     QList<QSharedPointer<BorderData> > m_bordersList; //Keep a copy of unique borders
diff --git a/tests/auto/styles/tst_stylestest.cpp b/tests/auto/styles/tst_stylestest.cpp
index c806753..cd003bc 100644
--- a/tests/auto/styles/tst_stylestest.cpp
+++ b/tests/auto/styles/tst_stylestest.cpp
@@ -13,6 +13,7 @@ public:
 private Q_SLOTS:
     void testEmptyStyle();
     void testAddFormat();
+    void testAddFormat2();
     void testSolidFillBackgroundColor();
 };
 
@@ -42,6 +43,23 @@ void StylesTest::testAddFormat()
     QVERIFY2(xmlData.contains("<cellXfs count=\"2\">"), ""); //Note we have a default one
 }
 
+void StylesTest::testAddFormat2()
+{
+    QXlsx::Styles styles;
+
+    QXlsx::Format *format = styles.createFormat();
+    format->setNumberFormat("h:mm:ss AM/PM"); //builtin 19
+    styles.addFormat(format);
+
+    QCOMPARE(format->numberFormatIndex(), 19);
+
+    QXlsx::Format *format2 = styles.createFormat();
+    format2->setNumberFormat("aaaaa h:mm:ss AM/PM"); //custom
+    styles.addFormat(format2);
+
+    QCOMPARE(format2->numberFormatIndex(), 164);
+}
+
 // For a solid fill, Excel reverses the role of foreground and background colours
 void StylesTest::testSolidFillBackgroundColor()
 {