diff --git a/src/EPPlus/FormulaParsing/EpplusExcelDataProvider.cs b/src/EPPlus/FormulaParsing/EpplusExcelDataProvider.cs
index 922835df62..c51ca54c19 100644
--- a/src/EPPlus/FormulaParsing/EpplusExcelDataProvider.cs
+++ b/src/EPPlus/FormulaParsing/EpplusExcelDataProvider.cs
@@ -24,6 +24,7 @@ Date               Author                       Change
 using OfficeOpenXml.FormulaParsing.Ranges;
 using System.Runtime.InteropServices;
 using OfficeOpenXml.Utils.String;
+using OfficeOpenXml.Style;
 
 namespace OfficeOpenXml.FormulaParsing
 {
@@ -641,7 +642,21 @@ public override string GetFormat(object value, string format, out bool isValidFo
             {
                 isValidFormat = true;
                 var ws = _currentWorksheet ?? _context.CurrentWorksheet;
-                var arg = new NumberFormatToTextArgs(ws, _context.CurrentCell.Row, _context.CurrentCell.Column, value, ws.GetStyleInner(_context.CurrentCell.Row, _context.CurrentCell.Column));
+
+                var existingId = ExcelNumberFormat.GetFromBuildIdFromFormat(format);
+
+                NumberFormatToTextArgs arg;
+                if (existingId == int.MinValue)
+                {
+                    //The format does not have a corresponding styleId
+                    //Still allow the NumberFormatToTextHandler to see the format
+                    arg = new NumberFormatToTextArgs(ws, _context.CurrentCell.Row, _context.CurrentCell.Column, value, format);
+                }
+                else
+                {
+                    arg = new NumberFormatToTextArgs(ws, _context.CurrentCell.Row, _context.CurrentCell.Column, value, existingId);
+                }
+                arg.FromFormula = true;
                 return _workbook.NumberFormatToTextHandler(arg);
             }
         }
diff --git a/src/EPPlus/NumberFormatToTextArgs.cs b/src/EPPlus/NumberFormatToTextArgs.cs
index a4a3ec55d7..1bbfbe8b66 100644
--- a/src/EPPlus/NumberFormatToTextArgs.cs
+++ b/src/EPPlus/NumberFormatToTextArgs.cs
@@ -12,6 +12,7 @@ Date               Author                       Change
  *************************************************************************************************/
 using OfficeOpenXml.FormulaParsing.Excel.Functions.Text;
 using OfficeOpenXml.Style;
+using OfficeOpenXml.Style.Interfaces;
 using OfficeOpenXml.Style.XmlAccess;
 using OfficeOpenXml.Utils.String;
 
@@ -23,6 +24,32 @@ namespace OfficeOpenXml
     public class NumberFormatToTextArgs
     {
         internal int _styleId;
+
+        ExcelNumberFormatWithoutId fallbackNumberFormat = null;
+
+        /// <summary>
+        /// If these args are provided from a formula
+        /// </summary>
+        public bool FromFormula = false;
+
+        /// <summary>
+        /// Constructor when numberformat is not built in
+        /// </summary>
+        /// <param name="ws"></param>
+        /// <param name="row"></param>
+        /// <param name="column"></param>
+        /// <param name="value"></param>
+        /// <param name="numberFormat"></param>
+        internal NumberFormatToTextArgs(ExcelWorksheet ws, int row, int column, object value, string numberFormat)
+        {
+            Worksheet = ws;
+            Row = row;
+            Column = column;
+            Value = value;
+            _styleId = -1;
+            fallbackNumberFormat = new ExcelNumberFormatWithoutId(numberFormat);
+        }
+
         internal NumberFormatToTextArgs(ExcelWorksheet ws, int row, int column, object value, int styleId)
         {
             Worksheet = ws;
@@ -31,6 +58,7 @@ internal NumberFormatToTextArgs(ExcelWorksheet ws, int row, int column, object v
             Value = value;
             _styleId = styleId;            
         }
+
         /// <summary>
         /// The worksheet of the cell.
         /// </summary>
@@ -46,11 +74,18 @@ internal NumberFormatToTextArgs(ExcelWorksheet ws, int row, int column, object v
         /// <summary>
         /// The number format settings for the cell
         /// </summary>
-        public ExcelNumberFormatXml NumberFormat 
+        public IExcelNumberFormat NumberFormat 
         { 
             get 
             {
-                return ValueToTextHandler.GetNumberFormat(_styleId, Worksheet.Workbook.Styles);
+                if(fallbackNumberFormat != null)
+                {
+                    return fallbackNumberFormat;
+                }
+                else
+                {
+                    return ValueToTextHandler.GetNumberFormat(_styleId, Worksheet.Workbook.Styles);
+                }
             } 
         } 
         /// <summary>
@@ -64,6 +99,13 @@ public string Text
         {
             get
             { 
+                if(fallbackNumberFormat != null)
+                {
+                    var ft = new ExcelFormatTranslator(NumberFormat.Format, -1);
+                    bool isValidFormat = false;
+                    var frmt = ValueToTextHandler.FormatValue(Value, false, ft, null, out isValidFormat);
+                    return frmt;
+                }
                 return ValueToTextHandler.GetFormattedText(Value, Worksheet.Workbook, _styleId, false);
             }
         }
diff --git a/src/EPPlus/Style/Interfaces/IExcelNumberFormat.cs b/src/EPPlus/Style/Interfaces/IExcelNumberFormat.cs
new file mode 100644
index 0000000000..594b8b05aa
--- /dev/null
+++ b/src/EPPlus/Style/Interfaces/IExcelNumberFormat.cs
@@ -0,0 +1,23 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+
+namespace OfficeOpenXml.Style.Interfaces
+{
+    public interface IExcelNumberFormat
+    {        
+        /// <summary>
+        /// The numberformat string
+        /// </summary>
+        public string Format { get; }
+        /// <summary>
+        /// Number format Id
+        /// </summary>
+        public int NumFmtId { get; }
+        /// <summary>
+        /// If this numberformat is built in
+        /// </summary>
+        public bool BuildIn { get; }
+    }
+}
diff --git a/src/EPPlus/Style/XmlAccess/ExcelNumberFormatWithoutId.cs b/src/EPPlus/Style/XmlAccess/ExcelNumberFormatWithoutId.cs
new file mode 100644
index 0000000000..9b953ad1f6
--- /dev/null
+++ b/src/EPPlus/Style/XmlAccess/ExcelNumberFormatWithoutId.cs
@@ -0,0 +1,23 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using OfficeOpenXml.Style.Interfaces;
+
+namespace OfficeOpenXml.Style.XmlAccess
+{
+    internal class ExcelNumberFormatWithoutId : IExcelNumberFormat
+    {
+        internal ExcelNumberFormatWithoutId(string format) 
+        {
+            Format = format;
+            NumFmtId = -1;
+            BuildIn = false;
+        }
+        public string Format { get; private set; }
+
+        public int NumFmtId { get; private set; }
+
+        public bool BuildIn { get; private set; }
+    }
+}
diff --git a/src/EPPlus/Style/XmlAccess/ExcelNumberFormatXml.cs b/src/EPPlus/Style/XmlAccess/ExcelNumberFormatXml.cs
index 7b6c4a6653..a0c0eb650e 100644
--- a/src/EPPlus/Style/XmlAccess/ExcelNumberFormatXml.cs
+++ b/src/EPPlus/Style/XmlAccess/ExcelNumberFormatXml.cs
@@ -10,22 +10,23 @@ Date               Author                       Change
  *************************************************************************************************
   01/27/2020         EPPlus Software AB       Initial release EPPlus 5
  *************************************************************************************************/
+using OfficeOpenXml.Style.Interfaces;
+using OfficeOpenXml.Utils;
 using System;
 using System.Collections.Generic;
-using System.Text;
-using System.Xml;
 using System.Globalization;
-using System.Text.RegularExpressions;
-using OfficeOpenXml.Utils;
-using System.Runtime.InteropServices;
 using System.Linq;
+using System.Runtime.InteropServices;
+using System.Text;
+using System.Text.RegularExpressions;
+using System.Xml;
 
 namespace OfficeOpenXml.Style.XmlAccess
 {
     /// <summary>
     /// Xml access class for number customFormats
     /// </summary>
-    public sealed class ExcelNumberFormatXml : StyleXmlHelper
+    public sealed class ExcelNumberFormatXml : StyleXmlHelper, IExcelNumberFormat
     {
 
         internal ExcelNumberFormatXml(XmlNamespaceManager nameSpaceManager) : base(nameSpaceManager)
diff --git a/src/EPPlusTest/Drawing/Chart/ChartSeriesTest.cs b/src/EPPlusTest/Drawing/Chart/ChartSeriesTest.cs
index 353a22c52a..f6cea68a87 100644
--- a/src/EPPlusTest/Drawing/Chart/ChartSeriesTest.cs
+++ b/src/EPPlusTest/Drawing/Chart/ChartSeriesTest.cs
@@ -1,14 +1,22 @@
-using Microsoft.VisualStudio.TestTools.UnitTesting;
+using Castle.Components.DictionaryAdapter.Xml;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using Newtonsoft.Json;
 using OfficeOpenXml;
+using OfficeOpenXml.ConditionalFormatting;
 using OfficeOpenXml.Drawing;
 using OfficeOpenXml.Drawing.Chart;
 using OfficeOpenXml.Drawing.Chart.ChartEx;
+using OfficeOpenXml.Drawing.Interfaces;
+using OfficeOpenXml.FormulaParsing.Utilities;
+using OfficeOpenXml.Style;
 using System;
 using System.Collections.Generic;
 using System.Drawing;
 using System.Linq;
+using System.Runtime.CompilerServices;
 using System.Text;
 using System.Threading.Tasks;
+using System.Xml;
 
 namespace EPPlusTest.Drawing.Chart
 {
diff --git a/src/EPPlusTest/Issues/StylingIssues.cs b/src/EPPlusTest/Issues/StylingIssues.cs
index 6d0fa4bde0..1082c31630 100644
--- a/src/EPPlusTest/Issues/StylingIssues.cs
+++ b/src/EPPlusTest/Issues/StylingIssues.cs
@@ -8,6 +8,8 @@
 using System.IO;
 using System.Globalization;
 using OfficeOpenXml.Style;
+using OfficeOpenXml.FormulaParsing;
+
 namespace EPPlusTest
 {
 	[TestClass]
@@ -424,6 +426,85 @@ public void s1007()
             //SaveAndCleanup(p);
         }
 
+
+        [TestMethod]
+        public void s1005()
+        {
+            SwitchToCulture("de-DE");
+
+            //Set specific built-in formats
+            if (!ExcelPackageSettings.CultureSpecificBuildInNumberFormats.ContainsKey("de-DE"))
+            {
+                ExcelPackageSettings.CultureSpecificBuildInNumberFormats.Add("de-DE",
+                new Dictionary<int, string>
+                {
+                    {14,"dd.MM.yyyy"},
+                    {15,"dd. MMM yy"},
+                    {16,"dd. MMM"},
+                    {17,"MMM yy"},
+                    {18,"hh:mm AM/PM" },
+                    {22,"dd.MM.yyyy hh:mm"},
+                    {37,"#,##0;-#,##0"},
+                    {38,"#,##0;[Rot]-#,##0"},
+                    {39,"#,##0.00;-#,##0.00"},
+                    {40,"#,##0.00;[Rot]-#,##0.00"},
+                    {47,"mm:ss,f"}
+                });
+            }
+
+            using (var p = OpenTemplatePackage("s1005.xlsx"))
+            {
+                //AND use a Custom Number Format
+                //This caused issues in the Text.cs file when we ran Calculate
+                p.Workbook.NumberFormatToTextHandler = CustomNumberFormatToTextExample;
+
+                var ws1 = p.Workbook.Worksheets[1];
+
+                var origText = ws1.Cells["D8"].Text;
+
+                //Verify cell contents match when test was written
+                Assert.IsTrue(origText.Contains(".8000"));
+                Assert.IsTrue(origText.Contains("(26895559.000)"));
+                Assert.IsTrue(origText.Contains("69928453.64000"));
+
+                ws1.Cells["D8"].Calculate();
+                var cellRich = ws1.Cells["D8"].RichText.Text;
+
+                //Verify formatting has changed appropriately for calculated string
+                Assert.IsTrue(cellRich.Contains("0,80"));
+                Assert.IsTrue(cellRich.Contains("(26.895.559,00)"));
+                Assert.IsTrue(cellRich.Contains("69.928.453,64"));
+
+                SaveAndCleanup(p);
+            }
+
+            SwitchBackToCurrentCulture();
+        }
+
+        private static string CustomNumberFormatToTextExample(NumberFormatToTextArgs options)
+        {
+            var result = options.Text;
+
+            switch (options.Value)
+            {
+                case DateTime dt:
+                    {
+                        switch (options.NumberFormat.Format)
+                        {
+                            case "dd. mmm yy":
+                                result = dt.ToString("dd. mmm yy"); //Return your own formatted text. Example
+                                break;
+                            default:
+                                result = dt.ToString(options.NumberFormat.Format);
+                                break;
+                        }
+                        break;
+                    }
+            }
+
+            return result;
+        }
+
         public class TestData
         {
             public int Id { get; set; }