diff --git a/src/backup.rs b/src/backup.rs
index afbde587..d2ae4ce3 100644
--- a/src/backup.rs
+++ b/src/backup.rs
@@ -284,6 +284,8 @@ impl BackupWriter {
         self.stats.files += 1;
         monitor.count(Counter::Files, 1);
         let apath = source_entry.apath();
+        let size = source_entry.size().expect("source entry has a size");
+        self.stats.source_files_bytes += size;
         trace!(?apath, "Copying file");
         let result = if let Some(basis_entry) = basis_entry {
             if content_heuristically_unchanged(source_entry, basis_entry) {
@@ -293,6 +295,7 @@ impl BackupWriter {
                     .all(|addr| self.block_dir.contains(&addr.hash))
                 {
                     self.stats.unmodified_files += 1;
+                    self.stats.source_unchanged_files_bytes += size;
                     let new_entry = IndexEntry {
                         addrs: basis_entry.addrs.clone(),
                         ..IndexEntry::metadata_from(source_entry)
@@ -308,19 +311,21 @@ impl BackupWriter {
                 } else {
                     warn!(%apath, ?basis_entry.addrs, "Some referenced blocks are missing or truncated; file will be stored again");
                     self.stats.modified_files += 1;
+                    self.stats.source_modified_files_bytes += size;
                     self.stats.replaced_damaged_blocks += 1;
                     Some(EntryChange::changed(basis_entry, source_entry))
                 }
             } else {
                 self.stats.modified_files += 1;
+                self.stats.source_modified_files_bytes += size;
                 Some(EntryChange::changed(basis_entry, source_entry))
             }
         } else {
             self.stats.new_files += 1;
+            self.stats.source_new_files_bytes += size;
             trace!("New file");
             Some(EntryChange::added(source_entry))
         };
-        let size = source_entry.size().expect("source entry has a size");
         if size == 0 {
             self.index_writer
                 .push_entry(IndexEntry::metadata_from(source_entry));
@@ -570,7 +575,6 @@ fn content_heuristically_unchanged<E: EntryTrait, O: EntryTrait>(
 
 #[derive(Add, AddAssign, Debug, Default, Eq, PartialEq, Clone)]
 pub struct BackupStats {
-    // TODO: Include source file bytes, including unmodified files.
     pub files: usize,
     pub symlinks: usize,
     pub directories: usize,
@@ -584,6 +588,15 @@ pub struct BackupStats {
     /// some of their blocks were damaged.
     pub replaced_damaged_blocks: usize,
 
+    /// Total bytes in all source files.
+    pub source_files_bytes: u64,
+    /// Bytes in unchanged files.
+    pub source_unchanged_files_bytes: u64,
+    /// Bytes in new files.
+    pub source_new_files_bytes: u64,
+    /// Bytes in modified files.
+    pub source_modified_files_bytes: u64,
+
     /// Bytes that matched an existing block.
     pub deduplicated_bytes: u64,
     /// Bytes that were stored as new blocks, before compression.
@@ -620,6 +633,12 @@ impl fmt::Display for BackupStats {
         write_count(w, "unsupported file kind", self.unknown_kind);
         writeln!(w).unwrap();
 
+        write_size(w, "source tree size:", self.source_files_bytes);
+        write_size(w, "  unchanged files", self.source_unchanged_files_bytes);
+        write_size(w, "  modified files", self.source_modified_files_bytes);
+        write_size(w, "  new files", self.source_new_files_bytes);
+        writeln!(w).unwrap();
+
         write_count(w, "files stored:", self.new_files + self.modified_files);
         write_count(w, "  empty files", self.empty_files);
         write_count(w, "  small combined files", self.small_combined_files);
@@ -670,6 +689,43 @@ mod test {
 
     use super::*;
 
+    #[tokio::test]
+    async fn source_tree_size_in_stats() {
+        let archive = Archive::create_temp().await;
+        let src = TreeFixture::new();
+        let monitor = TestMonitor::arc();
+
+        // Create files with known sizes
+        src.create_file_with_contents("file1", b"hello"); // 5 bytes
+        src.create_file_with_contents("file2", b"world!!!"); // 8 bytes
+        src.create_file_with_contents("file3", b"testing backup stats feature"); // 28 bytes
+
+        let stats = backup(&archive, src.path(), &BackupOptions::default(), monitor.clone())
+            .await
+            .unwrap();
+
+        // All files are new
+        assert_eq!(stats.new_files, 3);
+        assert_eq!(stats.source_files_bytes, 41); // 5 + 8 + 28
+        assert_eq!(stats.source_new_files_bytes, 41);
+        assert_eq!(stats.source_modified_files_bytes, 0);
+        assert_eq!(stats.source_unchanged_files_bytes, 0);
+
+        // Second backup - modify one file
+        src.create_file_with_contents("file2", b"changed content here"); // 20 bytes
+
+        let stats2 = backup(&archive, src.path(), &BackupOptions::default(), monitor.clone())
+            .await
+            .unwrap();
+
+        assert_eq!(stats2.modified_files, 1);
+        assert_eq!(stats2.unmodified_files, 2);
+        assert_eq!(stats2.source_files_bytes, 53); // 5 + 20 + 28
+        assert_eq!(stats2.source_new_files_bytes, 0);
+        assert_eq!(stats2.source_modified_files_bytes, 20);
+        assert_eq!(stats2.source_unchanged_files_bytes, 33); // 5 + 28
+    }
+
     #[tokio::test]
     async fn deleted_files_are_reported() {
         // tracing_subscriber::fmt::init();