diff --git a/src/data/move.ts b/src/data/move.ts
index 26b182ec5db..18f4b220911 100644
--- a/src/data/move.ts
+++ b/src/data/move.ts
@@ -1866,11 +1866,14 @@ export class HalfSacrificialAttr extends MoveEffectAttr {
 export class AddSubstituteAttr extends MoveEffectAttr {
   /** The ratio of the user's max HP that is required to apply this effect */
   private hpCost: number;
+  /** Whether the damage taken should be rounded up (Shed Tail rounds up) */
+  private roundUp: boolean;
 
-  constructor(hpCost: number = 0.25) {
+  constructor(hpCost: number, roundUp: boolean) {
     super(true);
 
     this.hpCost = hpCost;
+    this.roundUp = roundUp;
   }
 
   /**
@@ -1886,7 +1889,8 @@ export class AddSubstituteAttr extends MoveEffectAttr {
       return false;
     }
 
-    user.damageAndUpdate(Math.floor(user.getMaxHp() * this.hpCost), HitResult.OTHER, false, true, true);
+    const damageTaken = this.roundUp ? Math.ceil(user.getMaxHp() * this.hpCost) : Math.floor(user.getMaxHp() * this.hpCost);
+    user.damageAndUpdate(damageTaken, HitResult.OTHER, false, true, true);
     user.addTag(BattlerTagType.SUBSTITUTE, 0, move.id, user.id);
     return true;
   }
@@ -1899,7 +1903,7 @@ export class AddSubstituteAttr extends MoveEffectAttr {
   }
 
   getCondition(): MoveConditionFunc {
-    return (user, target, move) => !user.getTag(SubstituteTag) && user.hp > Math.floor(user.getMaxHp() * this.hpCost) && user.getMaxHp() > 1;
+    return (user, target, move) => !user.getTag(SubstituteTag) && user.hp > (this.roundUp ? Math.ceil(user.getMaxHp() * this.hpCost) : Math.floor(user.getMaxHp() * this.hpCost)) && user.getMaxHp() > 1;
   }
 
   /**
@@ -9036,7 +9040,7 @@ export function initMoves() {
       .attr(HighCritAttr)
       .slicingMove(),
     new SelfStatusMove(Moves.SUBSTITUTE, Type.NORMAL, -1, 10, -1, 0, 1)
-      .attr(AddSubstituteAttr),
+      .attr(AddSubstituteAttr, 0.25, false),
     new AttackMove(Moves.STRUGGLE, Type.NORMAL, MoveCategory.PHYSICAL, 50, -1, 1, -1, 0, 1)
       .attr(RecoilAttr, true, 0.25, true)
       .attr(TypelessAttr)
@@ -11382,7 +11386,7 @@ export function initMoves() {
       .attr(MovePowerMultiplierAttr, (user, target, move) => target.getAttackTypeEffectiveness(move.type, user) >= 2 ? 5461 / 4096 : 1)
       .makesContact(),
     new SelfStatusMove(Moves.SHED_TAIL, Type.NORMAL, -1, 10, -1, 0, 9)
-      .attr(AddSubstituteAttr, 0.5)
+      .attr(AddSubstituteAttr, 0.5, true)
       .attr(ForceSwitchOutAttr, true, SwitchType.SHED_TAIL)
       .condition(failIfLastInPartyCondition),
     new SelfStatusMove(Moves.CHILLY_RECEPTION, Type.ICE, -1, 10, -1, 0, 9)
diff --git a/test/moves/shed_tail.test.ts b/test/moves/shed_tail.test.ts
index 37f046ba2fa..be746aacd78 100644
--- a/test/moves/shed_tail.test.ts
+++ b/test/moves/shed_tail.test.ts
@@ -46,11 +46,8 @@ describe("Moves - Shed Tail", () => {
 
     expect(feebas).not.toBe(magikarp);
     expect(feebas.hp).toBe(feebas.getMaxHp());
-    // Note: Shed Tail's HP cost is currently not accurate to mainline, as it
-    // should cost ceil(maxHP / 2) instead of max(floor(maxHp / 2), 1). The current
-    // implementation is consistent with Substitute's HP cost logic, but that's not
-    // the case in mainline for some reason :regiDespair:.
-    expect(magikarp.hp).toBe(Math.ceil(magikarp.getMaxHp() / 2));
+    // Note: Altered the test to be consistent with the correct HP cost :yipeevee_static:
+    expect(magikarp.hp).toBe(Math.floor(magikarp.getMaxHp() / 2));
     expect(substituteTag).toBeDefined();
     expect(substituteTag?.hp).toBe(Math.floor(magikarp.getMaxHp() / 4));
   });