diff --git a/onnxruntime/core/providers/cpu/rnn/deep_cpu_lstm.cc b/onnxruntime/core/providers/cpu/rnn/deep_cpu_lstm.cc
index 4a197a59e0..f8a8b7dac8 100644
--- a/onnxruntime/core/providers/cpu/rnn/deep_cpu_lstm.cc
+++ b/onnxruntime/core/providers/cpu/rnn/deep_cpu_lstm.cc
@@ -849,7 +849,9 @@ void UniDirectionalLstm<T>::Compute(const gsl::span<const T>& inputs_arg,
       }
     };
 
-    double cost = max_sequence_length * fused_hidden_rows;  // TODO: approximate cost, needs more tuning.
+    // Approximate worst case cost of hidden_gemm_and_activations.
+    double gemm_cost = fused_hidden_rows * hidden_size_x4 * hidden_size_;
+    double cost = max_sequence_length * (gemm_cost + fused_hidden_rows);
     ExecuteLambdaInParallel(hidden_gemm_and_activations, batch_size_, fused_hidden_rows, cost, mlas_tp_);
 
   } else {