diff --git a/src/ThisAssembly.Strings/CSharp.sbntxt b/src/ThisAssembly.Strings/CSharp.sbntxt
index 10921ee3..df7ba476 100644
--- a/src/ThisAssembly.Strings/CSharp.sbntxt
+++ b/src/ThisAssembly.Strings/CSharp.sbntxt
@@ -28,18 +28,22 @@
         {{~ if value.IsIndexedFormat ~}}
         {{- summary value ~}}
 	    public static string {{ value.Id }}(
-            {{- for arg in value.Format -}}
+            {{- for arg in value.Args -}}
             object arg{{~ arg ~}}{{ if !for.last }}, {{ end }}
             {{- end -}}) 
             => string.Format(
                 CultureInfo.CurrentCulture,
-                Strings.GetResourceManager("{{ $1 }}").GetString("{{ value.Name }}"),
+                Strings.GetResourceManager("{{ $1 }}").GetString("{{ value.Name }}")
+                {{~ if value.HasArgFormat ~}}
+                {{- for arg in value.Format }}
+                .Replace("{{ arg.Value }}", "{%{{}%}{{ for.index }}{%{}}%}"){{- end -}}
+                {{~ end ~}},
                 {{ for arg in value.Format -}}
-                arg{{- arg -}}{{- if !for.last -}}, {{ end }}{{- end -}});
+                {{- if arg.Format -}}((IFormattable)arg{{- arg.Arg -}}).ToString("{{ arg.Format }}", CultureInfo.CurrentCulture){{- else -}}arg{{- arg.Arg -}}{{- end -}}{{- if !for.last -}}, {{ end }}{{- end -}});
         {{~ else if value.IsNamedFormat ~}}
         {{- summary value ~}}
 	    public static string {{ value.Id }}(
-            {{- for arg in value.Format -}}
+            {{- for arg in value.Args -}}
             object {{ arg ~}}{{ if !for.last }}, {{ end }}
             {{- end -}}) 
             => string.Format(
@@ -48,9 +52,9 @@
                     .GetResourceManager("{{ $1 }}")
                     .GetString("{{ value.Name }}")
                     {{- for arg in value.Format }}
-                    .Replace("{%{{}%}{{ arg }}{%{}}%}", "{%{{}%}{{ for.index }}{%{}}%}"){{- end -}},
+                    .Replace("{{ arg.Value }}", "{%{{}%}{{ for.index }}{%{}}%}"){{- end -}},
                 {{ for arg in value.Format -}}
-                {{- arg -}}{{- if !for.last -}}, {{ end }}{{- end -}});
+                {{- if arg.Format -}}((IFormattable){{- arg.Arg -}}).ToString("{{ arg.Format }}", CultureInfo.CurrentCulture){{- else -}}{{- arg.Arg -}}{{- end -}}{{- if !for.last -}}, {{ end }}{{- end -}});
 
         {{~ end ~}}
         {{~ end ~}}
diff --git a/src/ThisAssembly.Strings/Model.cs b/src/ThisAssembly.Strings/Model.cs
index f34f306f..561c74ba 100644
--- a/src/ThisAssembly.Strings/Model.cs
+++ b/src/ThisAssembly.Strings/Model.cs
@@ -14,7 +14,7 @@ record Model(ResourceArea RootArea, string ResourceName)
 
 static class ResourceFile
 {
-    static readonly Regex FormatExpression = new("{(?<name>[^{}]+)}", RegexOptions.Compiled);
+    static readonly Regex FormatExpression = new("{(?<arg>[^:{}]+)(?::(?<format>[^{}]+))?}", RegexOptions.Compiled);
     internal static readonly Regex NameReplaceExpression = new(@"\||:|;|\>|\<", RegexOptions.Compiled);
 
     public static ResourceArea Load(string fileName, string rootArea)
@@ -115,7 +115,12 @@ static ResourceValue GetValue(string resourceId, string resourceName, string res
             value.Format.AddRange(FormatExpression
                     .Matches(resourceValue)
                     .OfType<Match>()
-                    .Select(match => match.Groups["name"].Value)
+                    .Select(match =>
+                    {
+                        var arg = match.Groups["arg"].Value;
+                        var format = match.Groups["format"].Value;
+                        return new ArgFormat(match.Value, arg, string.IsNullOrWhiteSpace(format) ? null : format);
+                    })
                     .Distinct());
         }
 
@@ -135,10 +140,14 @@ record ResourceValue(string Id, string Name, string? Raw)
 {
     public string? Value => Raw?.Replace(Environment.NewLine, "")?.Replace("<", "&lt;")?.Replace(">", "&gt;");
     public string? Comment { get; init; }
-    public bool HasFormat => Format != null && Format.Count > 0;
+    public bool HasFormat => Format.Count > 0;
+    public bool HasArgFormat => Format.Any(x => x.Format != null);
     // We either have *all* named or all indexed. Can't mix. We'll skip generating 
     // methods for mixed ones and report as an analyzer error on the Resx.
-    public bool IsNamedFormat => HasFormat && Format.All(x => !int.TryParse(x, out _));
-    public bool IsIndexedFormat => HasFormat && Format.All(x => int.TryParse(x, out _));
-    public List<string> Format { get; } = new List<string>();
-}
\ No newline at end of file
+    public bool IsNamedFormat => HasFormat && Format.All(x => !int.TryParse(x.Arg, out _));
+    public bool IsIndexedFormat => HasFormat && Format.All(x => int.TryParse(x.Arg, out _));
+    public List<ArgFormat> Format { get; } = [];
+    public HashSet<string> Args => new(Format.Select(x => x.Arg));
+}
+
+record ArgFormat(string Value, string Arg, string? Format);
\ No newline at end of file
diff --git a/src/ThisAssembly.Strings/readme.md b/src/ThisAssembly.Strings/readme.md
index 4966e030..04163a30 100644
--- a/src/ThisAssembly.Strings/readme.md
+++ b/src/ThisAssembly.Strings/readme.md
@@ -18,6 +18,7 @@ Given the following Resx file:
 | Infrastructure_MissingService | Service {0} is required.              | For logging only! |
 | Shopping_NoShipping           | We cannot ship {0} to {1}.            |                   |
 | Shopping_OutOfStock           | Product is out of stock at this time. |                   |
+| Shopping_AvailableOn          | Product available on {date:yyyy-MM}.  |                   |
 
 The following code would be generated:
 
@@ -53,6 +54,14 @@ partial class ThisAssembly
             /// </summary>
             public static string OutOfStock
                 => Strings.GetResourceManager("ThisStore.Properties.Resources").GetString("OutOfStock");
+
+            /// <summary>
+            /// Product available on {date:yyyy-MM}.
+            /// </summary>
+            public static string AvailableOn(object date) 
+                => string.Format(CultureInfo.CurrentCulture, 
+                    Strings.GetResourceManager("ThisAssemblyTests.Resources").GetString("WithNamedFormat").Replace("{date:yyyy-MM}", "{0}"), 
+                    ((IFormattable)date).ToString("yyyy-MM", CultureInfo.CurrentCulture));
         }
     }
 }
diff --git a/src/ThisAssembly.Tests/Resources.resx b/src/ThisAssembly.Tests/Resources.resx
index 0c455cce..b1f6b08c 100644
--- a/src/ThisAssembly.Tests/Resources.resx
+++ b/src/ThisAssembly.Tests/Resources.resx
@@ -132,8 +132,14 @@
   <data name="Named" xml:space="preserve">
     <value>Hello {first}, {last}. Should we call you {first}?</value>
   </data>
+  <data name="WithIndexedFormat" xml:space="preserve">
+    <value>Year {0:yyyy}, Month {0:MM}</value>
+  </data>
+  <data name="WithNamedFormat" xml:space="preserve">
+    <value>Year {date:yyyy}, Month {date:MM}</value>
+  </data>
   <data name="WithNewLine" xml:space="preserve">
     <value>Hello, 
 World!</value>
-    </data>
+  </data>
 </root>
\ No newline at end of file
diff --git a/src/ThisAssembly.Tests/Tests.cs b/src/ThisAssembly.Tests/Tests.cs
index fe2f6b7f..91c31dc9 100644
--- a/src/ThisAssembly.Tests/Tests.cs
+++ b/src/ThisAssembly.Tests/Tests.cs
@@ -9,6 +9,7 @@ namespace ThisAssemblyTests;
 
 public record class Tests(ITestOutputHelper Output)
 {
+    DateTime dxt = DateTime.Now;
     [Fact]
     public void CanReadResourceFile()
         => Assert.NotNull(ResourceFile.Load("Resources.resx", "Strings"));
@@ -63,6 +64,14 @@ public void CanUseStringsNamedArguments()
     public void CanUseStringsIndexedArguments()
         => Assert.NotNull(ThisAssembly.Strings.Indexed("hello", "world"));
 
+    [Fact]
+    public void CanUseStringsNamedFormattedArguments()
+        => Assert.Equal("Year 2020, Month 03", ThisAssembly.Strings.WithNamedFormat(new DateTime(2020, 3, 20)));
+
+    [Fact]
+    public void CanUseStringsIndexedFormattedArguments()
+        => Assert.Equal("Year 2020, Month 03", ThisAssembly.Strings.WithIndexedFormat(new DateTime(2020, 3, 20)));
+
     [Fact]
     public void CanUseStringResource()
         => Assert.Equal("Value", ThisAssembly.Strings.Foo.Bar.Baz);