diff --git a/tgx/classes/graph.py b/tgx/classes/graph.py
index cd79fe8..b5afe9a 100644
--- a/tgx/classes/graph.py
+++ b/tgx/classes/graph.py
@@ -157,7 +157,22 @@ def max_nid(self) -> int:
                     max_id = u
                 if v > max_id:
                     max_id = v
-        return max_id + 1 #offset by 1
+        return max_id #offset by 1
+    
+    def min_nid(self) -> int:
+        r"""
+        find the smallest node ID in the dataset
+        """
+        edgelist = self.data
+        min_id = 1000000000
+        for _, edge_data in edgelist.items():
+            for u,v in edge_data.keys():
+                if u < min_id:
+                    min_id = u
+                if v < min_id:
+                    min_id = v
+        return min_id #offset by 1
+
     
     def map_nid(self) -> dict:
         r"""
diff --git a/tgx/utils/graph_utils.py b/tgx/utils/graph_utils.py
index b9b9023..270809a 100644
--- a/tgx/utils/graph_utils.py
+++ b/tgx/utils/graph_utils.py
@@ -14,6 +14,7 @@
 SEC_IN_WEEK = 86400 * 7
 SEC_IN_MONTH = 86400 * 30
 SEC_IN_YEAR = 86400 * 365
+SEC_IN_BIYEARLY = 86400 * 365 * 2
 
 # helper function to do ceiling divison, i.e. 5/2 = 3
 def ceiling_division(n, d):
@@ -57,6 +58,8 @@ def discretize_edges(edgelist: dict,
                 interval_size = SEC_IN_MONTH
             elif time_scale == "yearly":
                 interval_size = SEC_IN_YEAR
+            elif time_scale == "biyearly":
+                interval_size = SEC_IN_BIYEARLY
         else:
             raise TypeError("Invalid time interval")
     else: