diff --git a/conservancy_beancount/reports/core.py b/conservancy_beancount/reports/core.py
index dbf602da6b177c590b209fc3d759b00e90168bb7..d2cc8645de53be47f166c4303b9cad6b5a665e3c 100644
--- a/conservancy_beancount/reports/core.py
+++ b/conservancy_beancount/reports/core.py
@@ -368,6 +368,14 @@ class RelatedPostings(Sequence[data.Posting]):
     def balance_at_cost(self) -> Balance:
         return Balance(post.at_cost() for post in self)
 
+    def balance_at_cost_by_date(self, date: datetime.date) -> Balance:
+        for index, post in enumerate(self):
+            if post.meta.date >= date:
+                break
+        else:
+            index += 1
+        return Balance(post.at_cost() for post in self._postings[:index])
+
     def meta_values(self,
                     key: MetaKey,
                     default: Optional[MetaValue]=None,