diff --git a/src/TableCloth.Shared/Models/Configuration/X509CertPair.cs b/src/TableCloth.Shared/Models/Configuration/X509CertPair.cs
index 4c337076..642c2c42 100644
--- a/src/TableCloth.Shared/Models/Configuration/X509CertPair.cs
+++ b/src/TableCloth.Shared/Models/Configuration/X509CertPair.cs
@@ -2,6 +2,7 @@
 using System.Collections.Generic;
 using System.Linq;
 using System.Security.Cryptography.X509Certificates;
+using TableCloth.Resources;
 
 namespace TableCloth.Models.Configuration
 {
@@ -84,6 +85,34 @@ public X509CertPair(byte[] publicKey, byte[] privateKey)
 		public DateTime NotAfter { get; }
 		public DateTime NotBefore { get; }
 
+		public bool IsValid
+			=> NotBefore <= DateTime.Now && DateTime.Now <= NotAfter;
+
+        public bool HasExpired
+            => DateTime.Now > NotAfter;
+
+        public bool SoonExpire
+			=> DateTime.Now > NotAfter.Add(StringResources.Cert_ExpireWindow);
+
+		public string Availability
+		{
+			get
+			{
+				var now = DateTime.Now;
+				var expireWindow = StringResources.Cert_ExpireWindow;
+
+				if (now < NotBefore)
+					return StringResources.Cert_Availability_MayTooEarly(now, NotBefore);
+
+                if (now > NotAfter)
+                    return StringResources.Cert_Availability_Expired;
+                else if (now > NotAfter.Add(expireWindow))
+					return StringResources.Cert_Availability_ExpireSoon(now, NotAfter, expireWindow);
+
+				return StringResources.Cert_Availability_Available;
+			}
+		}
+
 		public string SubjectNameForNpkiApp
 			=> string.Join(",", Subject.Select(x => $"{x.Key.ToLowerInvariant()}={x.Value}"));
 
diff --git a/src/TableCloth.Shared/Resources/StringResources.cs b/src/TableCloth.Shared/Resources/StringResources.cs
index c24efc1f..db0f61f6 100644
--- a/src/TableCloth.Shared/Resources/StringResources.cs
+++ b/src/TableCloth.Shared/Resources/StringResources.cs
@@ -110,6 +110,31 @@ internal static string Get_AppVersion()
         }
     }
 
+    // 공동 인증서 관련 문자열들
+    partial class StringResources
+    {
+        internal static readonly TimeSpan Cert_ExpireWindow = TimeSpan.FromDays(-3d);
+
+        internal static string Cert_Availability_MayTooEarly(DateTime now, DateTime notBefore)
+            => $"{(int)Math.Truncate((notBefore - now).TotalDays)}일 후 사용 가능";
+
+        internal static string Cert_Availability_ExpireSoon(DateTime now, DateTime notAfter, TimeSpan expireWindow)
+            => $"{(int)Math.Truncate((now - (notAfter - expireWindow)).TotalDays)}일 후 만료";
+
+        internal static readonly string Cert_Availability_Expired = "만료됨";
+
+        internal static readonly string Cert_Availability_Available = "사용 가능";
+
+        internal static string Error_Cert_MayTooEarly(DateTime now, DateTime notBefore)
+            => $"선택하신 공동 인증서는 {(int)Math.Truncate((notBefore - now).TotalDays)}일 후부터 사용 가능합니다.";
+
+        internal static string Error_Cert_ExpireSoon(DateTime now, DateTime notAfter, TimeSpan expireWindow)
+            => $"{(int)Math.Truncate((now - (notAfter - expireWindow)).TotalDays)}일 후에 만료됩니다. 새로운 공동 인증서로 교체가 필요합니다.";
+
+        internal static readonly string Error_Cert_Expired
+            = $"선택하신 공동 인증서는 만료되었습니다. 다른 공동 인증서를 선택하거나, 새로운 공동 인증서로 교체 발급해야 합니다.";
+    }
+
     // 비 사용자 인터페이스 문자열들
     partial class StringResources
     {
@@ -301,15 +326,6 @@ internal static string Error_Cannot_Prepare_AppContents(Exception ex)
         
         internal static readonly string Info_ShortcutSuccess =
             "바탕 화면에 바로 가기를 생성했습니다.";
-
-        internal static string Error_Cert_MayTooEarly(DateTime notBefore)
-            => $"선택하신 공동 인증서는 {notBefore:yyyy년 M월 d일 tt h시 m분} 이후부터 사용 가능한 공동 인증서입니다. 인증서 사용이 불가능할 수 있습니다.";
-
-        internal static string Error_Cert_MayExpired(DateTime notAfter)
-            => $"선택하신 공동 인증서는 {notAfter:yyyy년 M월 d일 tt h시 m분} 이후부터는 사용이 불가능한 공동 인증서입니다. 인증서 사용이 불가능할 수 있습니다.";
-
-        internal static string Error_Cert_ExpireSoon(DateTime notAfter)
-            => $"선택하신 공동 인증서는 {notAfter:yyyy년 M월 d일 tt h시 m분} 이후부터는 사용이 불가능한 공동 인증서입니다. 공동 인증서 갱신을 준비하는 것이 좋습니다.";
     }
 
     // 스크립트 내에서 사용되는 문자열들
diff --git a/src/TableCloth/CertSelectWindow.xaml b/src/TableCloth/CertSelectWindow.xaml
index 4504e115..af6ccbf5 100644
--- a/src/TableCloth/CertSelectWindow.xaml
+++ b/src/TableCloth/CertSelectWindow.xaml
@@ -6,7 +6,7 @@
         mc:Ignorable="d"
         Style="{DynamicResource MainWindowStyle}"
         Title="{StaticResource CertSelectWindow_Title}" Width="480" Height="320"
-        MinWidth="480" MinHeight="320"
+        MinWidth="640" MinHeight="480"
         DataContext="{Binding CertSelectWindowViewModel, Source={StaticResource ViewModelLocator}}"
         TextOptions.TextFormattingMode="Display" TextOptions.TextRenderingMode="ClearType">
     <Grid>
@@ -26,9 +26,23 @@
 
             <TextBlock Grid.Row="0" TextWrapping="Wrap" Text="{StaticResource CertSelectWindow_InstructionLabel}" />
             <ListView Grid.Row="1" ItemsSource="{Binding Path='CertPairs'}" SelectedItem="{Binding Path='SelectedCertPair'}">
+                <ListView.ItemContainerStyle>
+                    <Style TargetType="ListViewItem">
+                        <Style.Triggers>
+                            <DataTrigger Binding="{Binding HasExpired}" Value="True">
+                                <Setter Property="Background">
+                                    <Setter.Value>
+                                        <Brush>#ffadad</Brush>
+                                    </Setter.Value>
+                                </Setter>
+                            </DataTrigger>
+                        </Style.Triggers>
+                    </Style>
+                </ListView.ItemContainerStyle>
                 <ListView.View>
                     <GridView>
                         <GridViewColumn Header="{StaticResource CertSelectWindow_CertList_CommonName}" Width="100" DisplayMemberBinding="{Binding CommonName}" />
+                        <GridViewColumn Header="{StaticResource CertSelectWindow_CertList_Available}" Width="100" DisplayMemberBinding="{Binding Availability}" />
                         <GridViewColumn Header="{StaticResource CertSelectWindow_CertList_OrganizationalUnits}" Width="100" DisplayMemberBinding="{Binding OrganizationalUnit}" />
                         <GridViewColumn Header="{StaticResource CertSelectWindow_CertList_Organization}" Width="100" DisplayMemberBinding="{Binding Organization}" />
                         <GridViewColumn Header="{StaticResource CertSelectWindow_CertList_CountryName}" Width="100" DisplayMemberBinding="{Binding CountryName}" />
@@ -40,11 +54,11 @@
                     <ColumnDefinition Width="1*" />
                     <ColumnDefinition Width="1*" />
                 </Grid.ColumnDefinitions>
-                <Button x:Name="ConvertToPfxButton" Grid.Column="0" HorizontalAlignment="Left" VerticalAlignment="Center" Content="{StaticResource CertSelectWindow_ConvertToPfxButtonText}" Click="ConvertToPfxButton_Click" />
-                <Button x:Name="RefreshCertPairsButton" Grid.Column="1" HorizontalAlignment="Right" VerticalAlignment="Center" Content="{StaticResource CertSelectWindow_RefreshButtonText}" Click="RefreshCertPairsButton_Click" />
+                <Button x:Name="ConvertToPfxButton" Grid.Column="0" HorizontalAlignment="Left" VerticalAlignment="Center" Content="{StaticResource CertSelectWindow_ConvertToPfxButtonText}" Click="ConvertToPfxButton_Click" Padding="5" />
+                <Button x:Name="RefreshCertPairsButton" Grid.Column="1" HorizontalAlignment="Right" VerticalAlignment="Center" Content="{StaticResource CertSelectWindow_RefreshButtonText}" Click="RefreshCertPairsButton_Click" Padding="5" />
             </Grid>
             <TextBlock Grid.Row="3" TextWrapping="Wrap" Text="{StaticResource CertSelectWindow_ManualInstructionLabelText}" />
-            <Button x:Name="OpenCertPairManuallyButton" Grid.Row="4" HorizontalAlignment="Left" VerticalAlignment="Top" Content="{StaticResource CertSelectWindow_OpenNpkiCertButton}" Margin="0 5 0 5" Click="OpenCertPairManuallyButton_Click" />
+            <Button x:Name="OpenCertPairManuallyButton" Grid.Row="4" HorizontalAlignment="Left" VerticalAlignment="Top" Content="{StaticResource CertSelectWindow_OpenNpkiCertButton}" Margin="0 5 0 5" Click="OpenCertPairManuallyButton_Click" Padding="5" />
         </Grid>
 
         <Grid Grid.Row="1">
diff --git a/src/TableCloth/MainWindow.xaml.cs b/src/TableCloth/MainWindow.xaml.cs
index d39168a9..a5b0eb2e 100644
--- a/src/TableCloth/MainWindow.xaml.cs
+++ b/src/TableCloth/MainWindow.xaml.cs
@@ -81,15 +81,16 @@ private void RunSandbox(TableClothConfiguration config)
         {
             if (config.CertPair != null)
             {
-                var today = DateTime.Now;
+                var now = DateTime.Now;
+                var expireWindow = StringResources.Cert_ExpireWindow;
 
-                if (today < config.CertPair.NotBefore)
-                    ViewModel.AppMessageBox.DisplayError(StringResources.Error_Cert_MayTooEarly(config.CertPair.NotBefore), false);
+                if (now < config.CertPair.NotBefore)
+                    ViewModel.AppMessageBox.DisplayError(StringResources.Error_Cert_MayTooEarly(now, config.CertPair.NotBefore), false);
 
-                if (today > config.CertPair.NotAfter)
-                    ViewModel.AppMessageBox.DisplayError(StringResources.Error_Cert_MayExpired(config.CertPair.NotAfter), false);
-                else if (today > config.CertPair.NotAfter.AddDays(-3d))
-                    ViewModel.AppMessageBox.DisplayInfo(StringResources.Error_Cert_ExpireSoon(config.CertPair.NotAfter));
+                if (now > config.CertPair.NotAfter)
+                    ViewModel.AppMessageBox.DisplayError(StringResources.Error_Cert_Expired, false);
+                else if (now > config.CertPair.NotAfter.Add(expireWindow))
+                    ViewModel.AppMessageBox.DisplayInfo(StringResources.Error_Cert_ExpireSoon(now, config.CertPair.NotAfter, expireWindow));
             }
 
             var tempPath = ViewModel.SharedLocations.GetTempPath();
diff --git a/src/TableCloth/Pages/DetailPage.xaml.cs b/src/TableCloth/Pages/DetailPage.xaml.cs
index 2fc20332..4d49b25f 100644
--- a/src/TableCloth/Pages/DetailPage.xaml.cs
+++ b/src/TableCloth/Pages/DetailPage.xaml.cs
@@ -70,15 +70,16 @@ private void RunSandbox(TableClothConfiguration config)
         {
             if (config.CertPair != null)
             {
-                var today = DateTime.Now;
+                var now = DateTime.Now;
+                var expireWindow = StringResources.Cert_ExpireWindow;
 
-                if (today < config.CertPair.NotBefore)
-                    ViewModel.AppMessageBox.DisplayError(StringResources.Error_Cert_MayTooEarly(config.CertPair.NotBefore), false);
+                if (now < config.CertPair.NotBefore)
+                    ViewModel.AppMessageBox.DisplayError(StringResources.Error_Cert_MayTooEarly(now, config.CertPair.NotBefore), false);
 
-                if (today > config.CertPair.NotAfter)
-                    ViewModel.AppMessageBox.DisplayError(StringResources.Error_Cert_MayExpired(config.CertPair.NotAfter), false);
-                else if (today > config.CertPair.NotAfter.AddDays(-3d))
-                    ViewModel.AppMessageBox.DisplayInfo(StringResources.Error_Cert_ExpireSoon(config.CertPair.NotAfter));
+                if (now > config.CertPair.NotAfter)
+                    ViewModel.AppMessageBox.DisplayError(StringResources.Error_Cert_Expired, false);
+                else if (now > config.CertPair.NotAfter.Add(expireWindow))
+                    ViewModel.AppMessageBox.DisplayInfo(StringResources.Error_Cert_ExpireSoon(now, config.CertPair.NotAfter, expireWindow));
             }
 
             var tempPath = ViewModel.SharedLocations.GetTempPath();
diff --git a/src/TableCloth/UIStringResources.xaml b/src/TableCloth/UIStringResources.xaml
index 465cdb46..f18bdd52 100644
--- a/src/TableCloth/UIStringResources.xaml
+++ b/src/TableCloth/UIStringResources.xaml
@@ -211,6 +211,10 @@
         소유자
     </system:String>
 
+    <system:String x:Key="CertSelectWindow_CertList_Available">
+        사용 가능 여부
+    </system:String>
+
     <system:String x:Key="CertSelectWindow_CertList_OrganizationalUnits">
         기관
     </system:String>