diff --git a/core/box/tiny_ptr_convert_box.h b/core/box/tiny_ptr_convert_box.h
new file mode 100644
index 00000000..e27ef827
--- /dev/null
+++ b/core/box/tiny_ptr_convert_box.h
@@ -0,0 +1,32 @@
+#ifndef HAKMEM_TINY_PTR_CONVERT_BOX_H
+#define HAKMEM_TINY_PTR_CONVERT_BOX_H
+
+#include <stddef.h>
+
+// Purpose: Zero-overhead inline conversions between BASE and USER pointers
+// Contract: Header is stored at offset -1 from USER pointer
+//
+// Example:
+//   - Allocation: base → user (user = base + 1)
+//   - Deallocation: user → base (base = user - 1)
+//
+// Offset definition (centralized for future extension)
+#define TINY_HEADER_OFFSET 1
+
+// Direct inline macros (zero cost, lvalue compatible in some contexts)
+#define tiny_base_to_user_inline(base) \
+    ((void*)((char*)(base) + TINY_HEADER_OFFSET))
+
+#define tiny_user_to_base_inline(user) \
+    ((void*)((char*)(user) - TINY_HEADER_OFFSET))
+
+// Verbose variants (for clarity in critical paths)
+static inline void* tiny_base_to_user(void* base) {
+    return tiny_base_to_user_inline(base);
+}
+
+static inline void* tiny_user_to_base(void* user) {
+    return tiny_user_to_base_inline(user);
+}
+
+#endif // HAKMEM_TINY_PTR_CONVERT_BOX_H
diff --git a/core/front/malloc_tiny_fast.h b/core/front/malloc_tiny_fast.h
index 01c6ec64..dc4c30d0 100644
--- a/core/front/malloc_tiny_fast.h
+++ b/core/front/malloc_tiny_fast.h
@@ -49,6 +49,7 @@
 #include "../box/tiny_c6_ultra_free_box.h" // Phase 4-2: C6 ULTRA-free (free-only, C6-only)
 #include "../box/tiny_ultra_classes_box.h" // Phase REFACTOR-1: Named constants for C6/C7
 #include "../box/tiny_legacy_fallback_box.h" // Phase REFACTOR-2: Legacy fallback logic unification
+#include "../box/tiny_ptr_convert_box.h" // Phase REFACTOR-3: Inline pointer macro centralization
 #include "../box/tiny_front_v3_env_box.h" // Tiny front v3 snapshot gate
 #include "../box/tiny_heap_env_box.h"   // ENV gate for TinyHeap front (A/B)
 #include "../box/tiny_route_env_box.h"  // Route snapshot (Heap vs Legacy)
@@ -177,7 +178,7 @@ static inline void* malloc_tiny_fast(size_t size) {
             FREE_PATH_STAT_INC(c6_ultra_alloc_hit);
             // BASE pointer のまま、USER pointer に変換して返す
             // (header は既に base[0] にある前提)
-            return (uint8_t*)base + 1;
+            return tiny_base_to_user_inline(base);
         }
     }
 
@@ -295,7 +296,7 @@ static inline int free_tiny_fast(void* ptr) {
     }
 
     // 4. BASE を計算して Unified Cache に push
-    void* base = (void*)((char*)ptr - 1);
+    void* base = tiny_user_to_base_inline(ptr);
     tiny_front_free_stat_inc(class_idx);
 
     // Phase FREE-LEGACY-BREAKDOWN-1: カウンタ散布 (1. 関数入口)