diff --git a/Sources/VRCKit/Extensions/DateFormatter+iso8601Full.swift b/Sources/VRCKit/Extensions/DateFormatter+iso8601Full.swift
index b0086bc..12d4772 100644
--- a/Sources/VRCKit/Extensions/DateFormatter+iso8601Full.swift
+++ b/Sources/VRCKit/Extensions/DateFormatter+iso8601Full.swift
@@ -16,4 +16,12 @@ public extension DateFormatter {
         formatter.locale = Locale(identifier: "en_US_POSIX")
         return formatter
     }()
+    
+    static let dateStringFormat: DateFormatter = {
+        let formatter = DateFormatter()
+        formatter.dateFormat = "yyy-MM-dd"
+        formatter.timeZone = TimeZone(secondsFromGMT: 0)
+        formatter.locale = Locale(identifier: "en_US_POSIX")
+        return formatter
+    }()
 }
diff --git a/Sources/VRCKit/Models/UserDetailModel.swift b/Sources/VRCKit/Models/UserDetailModel.swift
index 863346c..6a3f70f 100644
--- a/Sources/VRCKit/Models/UserDetailModel.swift
+++ b/Sources/VRCKit/Models/UserDetailModel.swift
@@ -25,7 +25,7 @@ public struct UserDetail: ProfileDetailRepresentable, LocationRepresentable {
     public let userIcon: URL?
     public let location: String
     public let friendKey: String
-    public let dateJoined: String
+    public let dateJoined: Date?
     public var note: String
     public let lastActivity: Date
 }
@@ -50,7 +50,8 @@ extension UserDetail: Codable {
         userIcon = try? container.decodeIfPresent(URL.self, forKey: .userIcon)
         location = try container.decode(String.self, forKey: .location)
         friendKey = try container.decode(String.self, forKey: .friendKey)
-        dateJoined = try container.decode(String.self, forKey: .dateJoined)
+        let dateJoinedString = try container.decode(String.self, forKey: .dateJoined)
+        dateJoined = DateFormatter.dateStringFormat.date(from: dateJoinedString)
         note = try container.decode(String.self, forKey: .note)
         lastActivity = try container.decode(Date.self, forKey: .lastActivity)
     }
diff --git a/Sources/VRCKit/Models/UserModel.swift b/Sources/VRCKit/Models/UserModel.swift
index 73be3e2..9b6b066 100644
--- a/Sources/VRCKit/Models/UserModel.swift
+++ b/Sources/VRCKit/Models/UserModel.swift
@@ -15,7 +15,7 @@ public struct User: ProfileDetailRepresentable {
     public let currentAvatar: String
     public let avatarImageUrl: URL?
     public let avatarThumbnailUrl: URL?
-    public let dateJoined: String
+    public let dateJoined: Date?
     public let displayName: String
     public let friendKey: String
     public let friends: [String]
@@ -63,7 +63,8 @@ extension User: Codable {
         currentAvatar = try container.decode(String.self, forKey: .currentAvatar)
         avatarImageUrl = try? container.decodeIfPresent(URL.self, forKey: .avatarImageUrl)
         avatarThumbnailUrl = try? container.decodeIfPresent(URL.self, forKey: .avatarThumbnailUrl)
-        dateJoined = try container.decode(String.self, forKey: .dateJoined)
+        let dateJoinedString = try container.decode(String.self, forKey: .dateJoined)
+        dateJoined = DateFormatter.dateStringFormat.date(from: dateJoinedString)
         displayName = try container.decode(String.self, forKey: .displayName)
         friendKey = try container.decode(String.self, forKey: .friendKey)
         friends = try container.decode([String].self, forKey: .friends)
diff --git a/Sources/VRCKit/PreviewServices/PreviewDataProvider.swift b/Sources/VRCKit/PreviewServices/PreviewDataProvider.swift
index 58d6f79..9a2c32d 100644
--- a/Sources/VRCKit/PreviewServices/PreviewDataProvider.swift
+++ b/Sources/VRCKit/PreviewServices/PreviewDataProvider.swift
@@ -67,7 +67,7 @@ final class PreviewDataProvider {
             currentAvatar: "",
             avatarImageUrl: nil,
             avatarThumbnailUrl: nil,
-            dateJoined: "2024/07/01",
+            dateJoined: Date(),
             displayName: "usr_\(previewUserId.uuidString.prefix(8))",
             friendKey: "",
             friends: friends.map(\.id),
@@ -162,7 +162,7 @@ final class PreviewDataProvider {
             userIcon: URL(string: "https://ul.h3z.jp/9gGIcerr.png"),
             location: location,
             friendKey: "",
-            dateJoined: "",
+            dateJoined: Date(),
             note: "",
             lastActivity: Date()
         )
diff --git a/Sources/VRCKit/Protocols/ProfileProtocols.swift b/Sources/VRCKit/Protocols/ProfileProtocols.swift
index d799c19..d3be836 100644
--- a/Sources/VRCKit/Protocols/ProfileProtocols.swift
+++ b/Sources/VRCKit/Protocols/ProfileProtocols.swift
@@ -30,7 +30,7 @@ public protocol ProfileElementRepresentable: Hashable, Identifiable {
 /// A protocol representing detailed profile properties for users.
 /// This protocol extends ProfileElementRepresentable and can be adopted by structures like User and UserDetail.
 public protocol ProfileDetailRepresentable: ProfileElementRepresentable {
-    var dateJoined: String { get }
+    var dateJoined: Date? { get }
     var lastActivity: Date { get }
     var state: User.State { get }
 }