diff --git a/PKHeX.Core/PKM/PK3.cs b/PKHeX.Core/PKM/PK3.cs
index f9f2d3a8a..b37415e7a 100644
--- a/PKHeX.Core/PKM/PK3.cs
+++ b/PKHeX.Core/PKM/PK3.cs
@@ -201,6 +201,8 @@ public override void RefreshChecksum()
             base.RefreshChecksum();
         }
 
+        protected override ushort CalculateChecksum() => PokeCrypto.GetCHK3(Data);
+
         public PK4 ConvertToPK4()
         {
             PK4 pk4 = new PK4 // Convert away!
diff --git a/PKHeX.Core/PKM/PKM.cs b/PKHeX.Core/PKM/PKM.cs
index b44e4382f..a4975f0df 100644
--- a/PKHeX.Core/PKM/PKM.cs
+++ b/PKHeX.Core/PKM/PKM.cs
@@ -39,21 +39,7 @@ public abstract class PKM : ITrainerID, ILangNick, IGameValueLimit, INature
 
         protected byte[] GetData(int Offset, int Length) => Data.Slice(Offset, Length);
 
-        protected virtual ushort CalculateChecksum()
-        {
-            ushort chk = 0;
-            switch (Format)
-            {
-                case 3:
-                    for (int i = 32; i < SIZE_STORED; i += 2)
-                        chk += BitConverter.ToUInt16(Data, i);
-                    return chk;
-                default: // 4+
-                    for (int i = 8; i < SIZE_STORED; i += 2)
-                        chk += BitConverter.ToUInt16(Data, i);
-                    return chk;
-            }
-        }
+        protected virtual ushort CalculateChecksum() => PokeCrypto.GetCHK(Data, SIZE_STORED);
 
         protected abstract byte[] Encrypt();
         public abstract int Format { get; }
diff --git a/PKHeX.Core/PKM/Util/PKMConverter.cs b/PKHeX.Core/PKM/Util/PKMConverter.cs
index 9d58b2f67..f44c4153c 100644
--- a/PKHeX.Core/PKM/Util/PKMConverter.cs
+++ b/PKHeX.Core/PKM/Util/PKMConverter.cs
@@ -78,7 +78,7 @@ public static int GetPKMDataFormat(byte[] data)
                 case PokeCrypto.SIZE_6PARTY: // collision with PGT, same size.
                     if (BitConverter.ToUInt16(data, 0x4) != 0) // Bad Sanity?
                         return -1;
-                    if (BitConverter.ToUInt32(data, 0x06) == PokeCrypto.GetCHK(data))
+                    if (BitConverter.ToUInt32(data, 0x06) == PokeCrypto.GetCHK(data, PokeCrypto.SIZE_6STORED))
                         return 6;
                     if (BitConverter.ToUInt16(data, 0x58) != 0) // Encrypted?
                     {
diff --git a/PKHeX.Core/PKM/Util/PokeCrypto.cs b/PKHeX.Core/PKM/Util/PokeCrypto.cs
index e13f9dce5..567de32c0 100644
--- a/PKHeX.Core/PKM/Util/PokeCrypto.cs
+++ b/PKHeX.Core/PKM/Util/PokeCrypto.cs
@@ -313,12 +313,12 @@ public static byte[] EncryptArray3(byte[] pkm)
         /// Gets the checksum of a 232 byte array.
         /// </summary>
         /// <param name="data">Decrypted Pokémon data.</param>
-        public static ushort GetCHK(byte[] data)
+        /// <param name="partyStart">Offset at which the Stored data ends and the Party data starts.</param>
+        public static ushort GetCHK(byte[] data, int partyStart)
         {
             ushort chk = 0;
-            for (int i = 8; i < SIZE_6STORED; i += 2)
+            for (int i = 8; i < partyStart; i += 2)
                 chk += BitConverter.ToUInt16(data, i);
-
             return chk;
         }