diff --git a/CHANGES b/CHANGES
index 4cb10f8a57e..2abf528a5a9 100644
--- a/CHANGES
+++ b/CHANGES
@@ -23,6 +23,7 @@ Bugs fixed
 * #10443: epub: EPUB builder can't detect the mimetype of .webp file
 * #10456: py domain: ``:meta:`` fields are displayed if docstring contains two
   or more meta-field
+* #9096: sphinx-build: the value of progress bar for paralle build is wrong
 
 Testing
 --------
diff --git a/sphinx/builders/__init__.py b/sphinx/builders/__init__.py
index 45188cd565c..d8500e11b42 100644
--- a/sphinx/builders/__init__.py
+++ b/sphinx/builders/__init__.py
@@ -25,6 +25,7 @@
 from sphinx.util.osutil import SEP, ensuredir, relative_uri, relpath
 from sphinx.util.parallel import ParallelTasks, SerialTasks, make_chunks, parallel_available
 from sphinx.util.tags import Tags
+from sphinx.util.typing import NoneType
 
 # side effect: registers roles and directives
 from sphinx import directives  # NOQA isort:skip
@@ -429,6 +430,13 @@ def _read_serial(self, docnames: List[str]) -> None:
             self.read_doc(docname)
 
     def _read_parallel(self, docnames: List[str], nproc: int) -> None:
+        chunks = make_chunks(docnames, nproc)
+
+        # create a status_iterator to step progressbar after reading a document
+        # (see: ``merge()`` function)
+        progress = status_iterator(chunks, __('reading sources... '), "purple",
+                                   len(chunks), self.app.verbosity)
+
         # clear all outdated docs at once
         for docname in docnames:
             self.events.emit('env-purge-doc', self.env, docname)
@@ -445,16 +453,15 @@ def merge(docs: List[str], otherenv: bytes) -> None:
             env = pickle.loads(otherenv)
             self.env.merge_info_from(docs, env, self.app)
 
-        tasks = ParallelTasks(nproc)
-        chunks = make_chunks(docnames, nproc)
+            next(progress)
 
-        for chunk in status_iterator(chunks, __('reading sources... '), "purple",
-                                     len(chunks), self.app.verbosity):
+        tasks = ParallelTasks(nproc)
+        for chunk in chunks:
             tasks.add_task(read_process, chunk, merge)
 
         # make sure all threads have finished
-        logger.info(bold(__('waiting for workers...')))
         tasks.join()
+        logger.info('')
 
     def read_doc(self, docname: str) -> None:
         """Parse a file and add/update inventory entries for the doctree."""
@@ -563,19 +570,26 @@ def write_process(docs: List[Tuple[str, nodes.document]]) -> None:
         tasks = ParallelTasks(nproc)
         chunks = make_chunks(docnames, nproc)
 
+        # create a status_iterator to step progressbar after writing a document
+        # (see: ``on_chunk_done()`` function)
+        progress = status_iterator(chunks, __('writing output... '), "darkgreen",
+                                   len(chunks), self.app.verbosity)
+
+        def on_chunk_done(args: List[Tuple[str, NoneType]], result: NoneType) -> None:
+            next(progress)
+
         self.app.phase = BuildPhase.RESOLVING
-        for chunk in status_iterator(chunks, __('writing output... '), "darkgreen",
-                                     len(chunks), self.app.verbosity):
+        for chunk in chunks:
             arg = []
             for docname in chunk:
                 doctree = self.env.get_and_resolve_doctree(docname, self)
                 self.write_doc_serialized(docname, doctree)
                 arg.append((docname, doctree))
-            tasks.add_task(write_process, arg)
+            tasks.add_task(write_process, arg, on_chunk_done)
 
         # make sure all threads have finished
-        logger.info(bold(__('waiting for workers...')))
         tasks.join()
+        logger.info('')
 
     def prepare_writing(self, docnames: Set[str]) -> None:
         """A place where you can add logic before :meth:`write_doc` is run"""
diff --git a/sphinx/util/__init__.py b/sphinx/util/__init__.py
index cd65b94b966..b5a49a9d118 100644
--- a/sphinx/util/__init__.py
+++ b/sphinx/util/__init__.py
@@ -13,8 +13,8 @@
 from importlib import import_module
 from os import path
 from time import mktime, strptime
-from typing import (IO, TYPE_CHECKING, Any, Callable, Dict, Iterable, Iterator, List, Optional,
-                    Pattern, Set, Tuple, Type)
+from typing import (IO, TYPE_CHECKING, Any, Callable, Dict, Generator, Iterable, List,
+                    Optional, Pattern, Set, Tuple, Type, TypeVar)
 from urllib.parse import parse_qsl, quote_plus, urlencode, urlsplit, urlunsplit
 
 from sphinx.errors import ExtensionError, FiletypeNotFoundError, SphinxParallelError
@@ -445,8 +445,12 @@ def display_chunk(chunk: Any) -> str:
     return str(chunk)
 
 
-def old_status_iterator(iterable: Iterable, summary: str, color: str = "darkgreen",
-                        stringify_func: Callable[[Any], str] = display_chunk) -> Iterator:
+T = TypeVar('T')
+
+
+def old_status_iterator(iterable: Iterable[T], summary: str, color: str = "darkgreen",
+                        stringify_func: Callable[[Any], str] = display_chunk
+                        ) -> Generator[T, None, None]:
     l = 0
     for item in iterable:
         if l == 0:
@@ -460,9 +464,10 @@ def old_status_iterator(iterable: Iterable, summary: str, color: str = "darkgree
 
 
 # new version with progress info
-def status_iterator(iterable: Iterable, summary: str, color: str = "darkgreen",
+def status_iterator(iterable: Iterable[T], summary: str, color: str = "darkgreen",
                     length: int = 0, verbosity: int = 0,
-                    stringify_func: Callable[[Any], str] = display_chunk) -> Iterable:
+                    stringify_func: Callable[[Any], str] = display_chunk
+                    ) -> Generator[T, None, None]:
     if length == 0:
         yield from old_status_iterator(iterable, summary, color, stringify_func)
         return