diff --git a/khaosz/config/train_config.py b/khaosz/config/train_config.py
index 6f8162f..28214da 100644
--- a/khaosz/config/train_config.py
+++ b/khaosz/config/train_config.py
@@ -34,6 +34,14 @@ class TrainConfig:
         default=4,
         metadata={"help": "Batch size for training."}
     )
+    start_epoch: int = field(
+        default=0,
+        metadata={"help": "Start epoch for training."}
+    )
+    start_batch: int = field(
+        default=0,
+        metadata={"help": "Start batch iteration for training."}
+    )
     checkpoint_interval: int = field(
         default=5000,
         metadata={"help": "Number of iterations between checkpoints."}
diff --git a/khaosz/trainer/train_callback.py b/khaosz/trainer/train_callback.py
index 5053bc0..1673221 100644
--- a/khaosz/trainer/train_callback.py
+++ b/khaosz/trainer/train_callback.py
@@ -161,7 +161,8 @@ class StepMonitorCallback(TrainCallback):
         Args:
             log_dir: Directory to save log files. If None, logs won't be saved to file.
             log_interval: Log every N steps
-            metrics: List of metrics to log. Supported: ['loss', 'lr', 'grad_norm', 'grad_std', grad_max', 'grad_min', 'grad_mean', 'grad_nan_num']
+            metrics: List of metrics to log. Supported: ['loss', 'lr', 'grad_norm', 'grad_std',
+                    grad_max', 'grad_min', 'grad_mean', 'grad_nan_num']
             custom_handlers: List of custom log handler functions
             json_log: Whether to save logs in JSON format
         """
diff --git a/khaosz/trainer/train_context.py b/khaosz/trainer/train_context.py
index 4248ce1..f0009b7 100644
--- a/khaosz/trainer/train_context.py
+++ b/khaosz/trainer/train_context.py
@@ -28,9 +28,10 @@ class TrainContext:
 class TrainContextBuilder:
     def __init__(self, trainer: 'Trainer'):
         self.trainer = trainer
-        self._context = TrainContext()
+        self._context: TrainContext = None
     
     def with_checkpoint(self, checkpoint: Optional[Checkpoint]) -> Self:
+        self._context = TrainContext()
         if checkpoint is None:
             checkpoint = Checkpoint(
                 model=self.trainer.parameter.model,
@@ -38,13 +39,17 @@ class TrainContextBuilder:
                 config=self.trainer.parameter.config,
             )
         else:
-            self._context.epoch = checkpoint.epoch
-            self._context.batch_iter = checkpoint.batch_iter
+            # resume from the assigned checkpoint or assigned iteration
+            self._context.epoch = max(checkpoint.epoch, self.trainer.train_config.start_epoch)
+            self._context.batch_iter = max(checkpoint.batch_iter, self.trainer.train_config.start_batch)
         
         self._context.checkpoint = checkpoint
         return self
     
     def with_optimizer(self) -> Self:
+        if self._context is None:
+            raise RuntimeError("Must call with_checkpoint() before with_optimizer()")
+        
         optimizer = self.trainer.train_config.optimizer
         
         if self._context.checkpoint and self._context.checkpoint.optimizer_state:
@@ -58,7 +63,9 @@ class TrainContextBuilder:
         return self
     
     def with_scheduler(self) -> Self:
-        # the build order has any problem ?
+        if not hasattr(self._context, 'optimizer') or self._context.optimizer is None:
+            raise RuntimeError("Must call with_optimizer() before with_scheduler()")
+
         optimizer = self.trainer.train_config.optimizer
         schedule_config = self.trainer.schedule_config
         scheduler = SchedulerFactory.load_scheduler(optimizer, schedule_config)
diff --git a/train.py b/train.py
index 93e3c88..c230f6d 100644
--- a/train.py
+++ b/train.py
@@ -24,6 +24,8 @@ def train(
     max_lr: int,
     n_epoch: int,
     batch_size: int,
+    start_epoch: int,
+    start_batch: int,
     accumulation_steps: int,
     warmup_steps: int,
     checkpoint_interval: int,
@@ -94,6 +96,8 @@ def train(
         checkpoint_dir=checkpoint_dir,
         n_epoch=n_epoch,
         batch_size=batch_size,
+        start_epoch=start_epoch,
+        start_batch=start_batch,
         checkpoint_interval=checkpoint_interval,
         accumulation_steps=accumulation_steps,
         max_grad_norm=max_grad_norm,
@@ -135,6 +139,8 @@ if __name__ == "__main__":
     parser.add_argument("--random_seed", type=int, default=3407, help="Random seed for reproducibility.")
     
     # other configs
+    parser.add_argument("--start_epoch", type=int, default=0, help="Start epoch for training.")
+    parser.add_argument("--start_batch", type=int, default=0, help="Start batch for training.")
     parser.add_argument("--resume_from_checkpoint", type=bool, default=False, help="train from checkpoint or not.")
     parser.add_argument("--multi_turn", type=bool, default=False, help="Whether to use multi-turn convsersation training.")
     parser.add_argument("--dpo_beta", type=float, default=0.1, help="DPO beta value.")