diff --git a/posted/_columns/fields.py b/posted/_columns/fields.py
index b13de647..c8722ab1 100644
--- a/posted/_columns/fields.py
+++ b/posted/_columns/fields.py
@@ -390,7 +390,7 @@ def _select(
                     .assign(
                         value=lambda row: (
                             row["value_lower"]
-                            + (row[f"{col_id}_upper"] - row[col_id])
+                            + (row[col_id] - row[f"{col_id}_lower"])
                             / (row[f"{col_id}_upper"] - row[f"{col_id}_lower"])
                             * (row["value_upper"] - row["value_lower"])
                         )