diff --git a/llm_bench/load_test.py b/llm_bench/load_test.py
index 174a903..fa23a74 100644
--- a/llm_bench/load_test.py
+++ b/llm_bench/load_test.py
@@ -162,13 +162,20 @@ def _create_dataset(cls, options: argparse.Namespace):
                     prompt = options.prompt
                 dataset_file = "code.txt"
 
+            if options.prompt_cache_max_len is not None:
+                common_tokens = options.prompt_cache_max_len
+            elif options.prompt_cache_max_pct is not None:
+                common_tokens = int(options.prompt_tokens * options.prompt_cache_max_pct / 100)
+            else:
+                common_tokens = 0
+
             return TranslationDataset(
                 path=os.path.join(os.path.dirname(os.path.abspath(__file__)), dataset_file),
                 prompt="\n\n" + prompt,
                 tokenizer_path=options.tokenizer,
                 chat=options.chat,
                 num_tokens=options.prompt_tokens,
-                common_tokens=options.prompt_cache_max_len,
+                common_tokens=common_tokens,
             )
         else:
             raise ValueError(f"Unknown dataset: {options.dataset}")
@@ -1451,8 +1458,11 @@ def init_parser(parser):
         "--prompt-cache-max-len",
         env_var="PROMPT_CACHE_MAX_LEN",
         type=int,
-        default=0,
-        help="Maximum length of the prompt cache to use. Defaults to 0 (no caching).",
+        default=None,
+        help="Maximum number of shared prefix tokens across requests. "
+        "If not specified but --prompt-cache-max-pct is set, auto-computed as "
+        "int(prompt_tokens * prompt_cache_max_pct / 100). Defaults to 0 (no shared prefix) "
+        "when neither this nor --prompt-cache-max-pct is provided.",
     )
     parser.add_argument(
         "--prompt-cache-max-pct",