diff --git a/finnow-api/source/transaction/data_impl_sqlite.d b/finnow-api/source/transaction/data_impl_sqlite.d
index 30b38f6..44e9293 100644
--- a/finnow-api/source/transaction/data_impl_sqlite.d
+++ b/finnow-api/source/transaction/data_impl_sqlite.d
@@ -223,9 +223,8 @@ class SqliteTransactionRepository : TransactionRepository {
 
         // 1. Get the total count of transactions that match the search filters.
         qb.select("COUNT (DISTINCT txn.id)");
-        applyFilters(qb, request);
+        applyFilters(qb, request, new SqliteTransactionCategoryRepository(db));
         string countQuery = qb.build();
-        // writeln(countQuery);
         Statement countStmt = db.prepare(countQuery);
         qb.applyArgBindings(countStmt);
         auto countResult = countStmt.execute();
diff --git a/finnow-api/source/transaction/search_filters.d b/finnow-api/source/transaction/search_filters.d
index 6883d25..1e9f735 100644
--- a/finnow-api/source/transaction/search_filters.d
+++ b/finnow-api/source/transaction/search_filters.d
@@ -14,17 +14,23 @@ import std.uri;
 import std.uni;
 
 import util.sqlite;
+import transaction.data;
 
 /**
  * Applies a set of filters to a query builder for searching over transactions.
  * Params:
  *   qb = The query builder to add WHERE clauses and argument bindings to.
  *   request = The request to get filter options from.
+ *   categoryRepo = Repository for fetching category data, which might be
+ *     needed if the user is filtering by a parent category.
  */
-void applyFilters(ref QueryBuilder qb, in ServerHttpRequest request) {
+void applyFilters(
+    ref QueryBuilder qb,
+    in ServerHttpRequest request,
+    TransactionCategoryRepository categoryRepo
+) {
     applyPropertyInFilter!string(qb, request, "tags.tag", "tag");
     applyPropertyInFilter!ulong(qb, request, "vendor.id", "vendor");
-    applyPropertyInFilter!ulong(qb, request, "category.id", "category");
     applyPropertyInFilter!string(qb, request, "txn.currency", "currency");
     applyPropertyInFilter!ulong(qb, request, "account_credit.id", "credited-account");
     applyPropertyInFilter!ulong(qb, request, "account_debit.id", "debited-account");
@@ -45,6 +51,25 @@ void applyFilters(ref QueryBuilder qb, in ServerHttpRequest request) {
         });
     }
 
+    // Separate filter that handles the hierarchical category relationship, so
+    // if a parent category is filtered, all children are also included.
+    if (request.hasParam("category")) {
+        ulong[] categoryIds = request.getParamValues!ulong("category");
+        auto app = appender!(ulong[]);
+        foreach (id; categoryIds) {
+            app ~= getAllPossibleCategoryIds(id, categoryRepo);
+        }
+        ulong[] allPossibleIds = app[];
+        if (allPossibleIds.length > 0) {
+            qb.where("(" ~ "txn.category_id = ?".repeat(allPossibleIds.length).join(" OR ") ~ ")");
+            qb.withArgBinding((ref stmt, ref idx) {
+                foreach (value; allPossibleIds) {
+                    stmt.bind(idx++, value);
+                }
+            });
+        }
+    }
+
     if (request.hasParam("min-amount")) {
         ulong[] values = request.getParamValues!ulong("min-amount");
         if (values.length > 0) {
@@ -140,3 +165,13 @@ private T[] getParamValues(T = string)(in ServerHttpRequest request, string key)
     }
     return [];
 }
+
+private ulong[] getAllPossibleCategoryIds(ulong parentId, TransactionCategoryRepository categoryRepo) {
+    auto app = appender!(ulong[]);
+    app ~= parentId;
+    foreach (child; categoryRepo.findAllByParentId(Optional!ulong.of(parentId))) {
+        app ~= child.id;
+        app ~= getAllPossibleCategoryIds(child.id, categoryRepo);
+    }
+    return app[];
+}