diff --git a/ftl/core/custom-study.ftl b/ftl/core/custom-study.ftl
index 06b61ff30..fd46d72c2 100644
--- a/ftl/core/custom-study.ftl
+++ b/ftl/core/custom-study.ftl
@@ -24,8 +24,11 @@ custom-study-select = Select
 custom-study-select-tags-to-exclude = Select tags to exclude:
 custom-study-selective-study = Selective Study
 custom-study-study-by-card-state-or-tag = Study by card state or tag
-custom-study-available-new-cards = Available new cards: { $count }
-custom-study-available-review-cards = Available review cards: { $count }
+custom-study-available-new-cards-2 = Available new cards: { $countString }
+custom-study-available-review-cards-2 = Available review cards: { $countString }
+custom-study-available-child-count = ({ $count } in subdecks)
 
 ## DEPRECATED - you do not need to translate these.
 
+custom-study-available-new-cards = Available new cards: { $count }
+custom-study-available-review-cards = Available review cards: { $count }
diff --git a/proto/anki/scheduler.proto b/proto/anki/scheduler.proto
index c8bbf419f..c133664ac 100644
--- a/proto/anki/scheduler.proto
+++ b/proto/anki/scheduler.proto
@@ -291,4 +291,7 @@ message CustomStudyDefaultsResponse {
   uint32 extend_review = 3;
   uint32 available_new = 4;
   uint32 available_review = 5;
+  // in v3, counts for children are provided separately
+  uint32 available_new_in_children = 6;
+  uint32 available_review_in_children = 7;
 }
diff --git a/qt/aqt/customstudy.py b/qt/aqt/customstudy.py
index 1c43ca69d..b6c359c82 100644
--- a/qt/aqt/customstudy.py
+++ b/qt/aqt/customstudy.py
@@ -1,6 +1,8 @@
 # Copyright: Ankitects Pty Ltd and contributors
 # License: GNU AGPL, version 3 or later; http://www.gnu.org/licenses/agpl.html
 
+from __future__ import annotations
+
 from typing import Tuple
 
 import aqt
@@ -75,6 +77,12 @@ class CustomStudy(QDialog):
         qconnect(f.radioPreview.clicked, lambda: self.onRadioChange(RADIO_PREVIEW))
         qconnect(f.radioCram.clicked, lambda: self.onRadioChange(RADIO_CRAM))
 
+    def count_with_children(self, parent: int, children: int) -> str:
+        if children:
+            return f"{parent} {tr.custom_study_available_child_count(children)}"
+        else:
+            return str(parent)
+
     def onRadioChange(self, idx: int) -> None:
         form = self.form
         min_spinner_value = 1
@@ -86,15 +94,21 @@ class CustomStudy(QDialog):
         ok = tr.custom_study_ok()
 
         if idx == RADIO_NEW:
-            title_text = tr.custom_study_available_new_cards(
-                count=self.defaults.available_new
+            title_text = tr.custom_study_available_new_cards_2(
+                count_string=self.count_with_children(
+                    self.defaults.available_new,
+                    self.defaults.available_new_in_children,
+                ),
             )
             text_before_spinner = tr.custom_study_increase_todays_new_card_limit_by()
             current_spinner_value = self.defaults.extend_new
             min_spinner_value = -DYN_MAX_SIZE
         elif idx == RADIO_REV:
-            title_text = tr.custom_study_available_review_cards(
-                count=self.defaults.available_review
+            title_text = tr.custom_study_available_review_cards_2(
+                count_string=self.count_with_children(
+                    self.defaults.available_review,
+                    self.defaults.available_review_in_children,
+                ),
             )
             text_before_spinner = tr.custom_study_increase_todays_review_limit_by()
             current_spinner_value = self.defaults.extend_review
diff --git a/qt/aqt/main.py b/qt/aqt/main.py
index b611e25f5..501e456b0 100644
--- a/qt/aqt/main.py
+++ b/qt/aqt/main.py
@@ -1,5 +1,6 @@
 # Copyright: Ankitects Pty Ltd and contributors
 # License: GNU AGPL, version 3 or later; http://www.gnu.org/licenses/agpl.html
+
 from __future__ import annotations
 
 import enum
diff --git a/rslib/src/scheduler/filtered/custom_study.rs b/rslib/src/scheduler/filtered/custom_study.rs
index e6090a311..73f368a6b 100644
--- a/rslib/src/scheduler/filtered/custom_study.rs
+++ b/rslib/src/scheduler/filtered/custom_study.rs
@@ -34,8 +34,29 @@ impl Collection {
             .deck_tree(Some(TimestampSecs::now()))?
             .get_deck(deck_id)
             .ok_or(AnkiError::NotFound)?;
-        let available_new = subtree.sum(|node| node.new_uncapped);
-        let available_review = subtree.sum(|node| node.review_uncapped);
+        let v3 = self.get_config_bool(BoolKey::Sched2021);
+        let available_new_including_children = subtree.sum(|node| node.new_uncapped);
+        let available_review_including_children = subtree.sum(|node| node.review_uncapped);
+        let (
+            available_new,
+            available_new_in_children,
+            available_review,
+            available_review_in_children,
+        ) = if v3 {
+            (
+                subtree.new_uncapped,
+                available_new_including_children - subtree.new_uncapped,
+                subtree.review_uncapped,
+                available_review_including_children - subtree.review_uncapped,
+            )
+        } else {
+            (
+                available_new_including_children,
+                0,
+                available_review_including_children,
+                0,
+            )
+        };
         // tags
         let include_tags: HashSet<String> = self.get_config_default(
             DeckConfigKey::CustomStudyIncludeTags
@@ -67,6 +88,8 @@ impl Collection {
             extend_review,
             available_new,
             available_review,
+            available_new_in_children,
+            available_review_in_children,
         })
     }
 }