diff --git a/src/calibre/db/backend.py b/src/calibre/db/backend.py
index 29b789b5f9..9001d2a050 100644
--- a/src/calibre/db/backend.py
+++ b/src/calibre/db/backend.py
@@ -1432,7 +1432,7 @@ class DB:
 
     @user_version.setter
     def user_version(self, val):
-        self.execute('PRAGMA user_version=%d'%int(val))
+        self.execute(f'PRAGMA user_version={int(val)}')
 
     def initialize_database(self):
         metadata_sqlite = P('metadata_sqlite.sql', data=True,
diff --git a/src/calibre/db/cli/cmd_restore_database.py b/src/calibre/db/cli/cmd_restore_database.py
index 88169e711e..ab4e75d11d 100644
--- a/src/calibre/db/cli/cmd_restore_database.py
+++ b/src/calibre/db/cli/cmd_restore_database.py
@@ -54,7 +54,7 @@ class Progress:
         if msg is None:
             self.total = float(step)
         else:
-            prints(msg, '...', '%d%%' % int(100 * (step / self.total)))
+            prints(msg, '...', f'{int(100*(step/self.total))}%')
 
 
 def main(opts, args, dbctx):
diff --git a/src/calibre/ebooks/metadata/__init__.py b/src/calibre/ebooks/metadata/__init__.py
index 19606d0fea..55d46a44c2 100644
--- a/src/calibre/ebooks/metadata/__init__.py
+++ b/src/calibre/ebooks/metadata/__init__.py
@@ -251,7 +251,7 @@ def fmt_sidx(i, fmt='%.2f', use_roman=False):
     except Exception:
         return str(i)
     if int(i) == i:
-        return roman(int(i)) if use_roman else '%d'%int(i)
+        return roman(int(i)) if use_roman else str(int(i))
     ans = fmt%i
     if '.' in ans:
         ans = ans.rstrip('0')
diff --git a/src/calibre/ebooks/mobi/mobiml.py b/src/calibre/ebooks/mobi/mobiml.py
index e60d7dc59e..75a0962969 100644
--- a/src/calibre/ebooks/mobi/mobiml.py
+++ b/src/calibre/ebooks/mobi/mobiml.py
@@ -160,8 +160,8 @@ class MobiMLizer:
             return ptsize
         embase = self.profile.fbase
         if round(ptsize) < embase:
-            return '%dpt' % int(round(ptsize))
-        return '%dem' % int(round(ptsize / embase))
+            return f'{int(round(ptsize))}pt'
+        return f'{int(round(ptsize/embase))}em'
 
     def preize_text(self, text, pre_wrap=False):
         text = str(text)
@@ -503,7 +503,7 @@ class MobiMLizer:
                 istate.attrib['width'] = raww
             else:
                 prop = style['width'] / self.profile.width
-                istate.attrib['width'] = '%d%%' % int(round(prop * 100))
+                istate.attrib['width'] = f'{int(round(prop*100))}%'
         elif display == 'table':
             tag = 'table'
         elif display == 'table-row':
diff --git a/src/calibre/ebooks/mobi/reader/mobi6.py b/src/calibre/ebooks/mobi/reader/mobi6.py
index 5554c6d58a..085fc2f42f 100644
--- a/src/calibre/ebooks/mobi/reader/mobi6.py
+++ b/src/calibre/ebooks/mobi/reader/mobi6.py
@@ -533,7 +533,7 @@ class MobiReader:
                             try:
                                 nval = float(val[:-2])
                                 nval *= 16 * (168.451/72)  # Assume this was set using the Kindle profile
-                                attrib[attr] = '%dpx'%int(nval)
+                                attrib[attr] = f'{int(nval)}px'
                             except:
                                 del attrib[attr]
                         elif val.lower().endswith('%'):
@@ -558,7 +558,7 @@ class MobiReader:
             if 'filepos' in attrib:
                 filepos = attrib.pop('filepos')
                 try:
-                    attrib['href'] = '#filepos%d' % int(filepos)
+                    attrib['href'] = f'#filepos{int(filepos)}'
                 except ValueError:
                     pass
             if (tag.tag == 'a' and attrib.get('id', '').startswith('filepos') and
diff --git a/src/calibre/ebooks/pdf/reflow.py b/src/calibre/ebooks/pdf/reflow.py
index ff82cffa22..de2b1a2d40 100644
--- a/src/calibre/ebooks/pdf/reflow.py
+++ b/src/calibre/ebooks/pdf/reflow.py
@@ -151,8 +151,7 @@ class Image(Element):
         self.align = 'L'
 
     def to_html(self):
-        return '<img src="%s" alt="" width="%dpx" height="%dpx"/>' % \
-                (self.src, int(self.width), int(self.height))
+        return f'<img src="{self.src}" alt="" width="{int(self.width)}px" height="{int(self.height)}px"/>'
 
     def dump(self, f):
         f.write(self.to_html())
diff --git a/src/calibre/gui2/dialogs/custom_recipes.py b/src/calibre/gui2/dialogs/custom_recipes.py
index 49c8356d5b..43a004c301 100644
--- a/src/calibre/gui2/dialogs/custom_recipes.py
+++ b/src/calibre/gui2/dialogs/custom_recipes.py
@@ -154,7 +154,7 @@ def py3_repr(x):
 
 
 def options_to_recipe_source(title, oldest_article, max_articles_per_feed, feeds):
-    classname = 'BasicUserRecipe%d' % int(time.time())
+    classname = f'BasicUserRecipe{int(time.time())}'
     title = str(title).strip() or classname
     indent = ' ' * 8
     if feeds:
diff --git a/src/calibre/gui2/linux_file_dialogs.py b/src/calibre/gui2/linux_file_dialogs.py
index 126b550db2..42b8d36092 100644
--- a/src/calibre/gui2/linux_file_dialogs.py
+++ b/src/calibre/gui2/linux_file_dialogs.py
@@ -233,7 +233,7 @@ def zenity_cmd(window, title, *rest):
     ans = ['zenity', '--modal', '--file-selection', '--title=' + title, '--separator=\n']
     winid = get_winid(window)
     if winid is not None:
-        ans += ['--attach=%d' % int(winid)]
+        ans += [f'--attach={int(winid)}']
     return ans + list(rest)
 
 
diff --git a/src/calibre/library/catalogs/epub_mobi_builder.py b/src/calibre/library/catalogs/epub_mobi_builder.py
index 7a00b1b0e5..948ea35bb2 100644
--- a/src/calibre/library/catalogs/epub_mobi_builder.py
+++ b/src/calibre/library/catalogs/epub_mobi_builder.py
@@ -1555,7 +1555,7 @@ class CatalogBuilder:
 
             aTag = soup.new_tag('a')
             if self.opts.generate_descriptions:
-                aTag['href'] = 'book_%d.html' % (int(float(book['id'])))
+                aTag['href'] = 'book_{}.html'.format(int(float(book['id'])))
 
             # Generate the title from the template
             args = self.generate_format_args(book)
@@ -1706,7 +1706,7 @@ class CatalogBuilder:
 
                     aTag = soup.new_tag('a')
                     if self.opts.generate_descriptions:
-                        aTag['href'] = 'book_%d.html' % (int(float(new_entry['id'])))
+                        aTag['href'] = 'book_{}.html'.format(int(float(new_entry['id'])))
 
                     # Generate the title from the template
                     args = self.generate_format_args(new_entry)
@@ -1758,7 +1758,7 @@ class CatalogBuilder:
 
                     aTag = soup.new_tag('a')
                     if self.opts.generate_descriptions:
-                        aTag['href'] = 'book_%d.html' % (int(float(new_entry['id'])))
+                        aTag['href'] = 'book_{}.html'.format(int(float(new_entry['id'])))
 
                     # Generate the title from the template
                     args = self.generate_format_args(new_entry)
@@ -1923,7 +1923,7 @@ class CatalogBuilder:
 
                     aTag = soup.new_tag('a')
                     if self.opts.generate_descriptions:
-                        aTag['href'] = 'book_%d.html' % (int(float(new_entry['id'])))
+                        aTag['href'] = 'book_{}.html'.format(int(float(new_entry['id'])))
                     aTag.insert(0, NavigableString(new_entry['title']))
                     pBookTag.insert(ptc, aTag)
                     ptc += 1
@@ -1972,7 +1972,7 @@ class CatalogBuilder:
 
                     aTag = soup.new_tag('a')
                     if self.opts.generate_descriptions:
-                        aTag['href'] = 'book_%d.html' % (int(float(new_entry['id'])))
+                        aTag['href'] = 'book_{}.html'.format(int(float(new_entry['id'])))
                     aTag.insert(0, NavigableString(new_entry['title']))
                     pBookTag.insert(ptc, aTag)
                     ptc += 1
@@ -2274,7 +2274,7 @@ class CatalogBuilder:
             # Add the book title
             aTag = soup.new_tag('a')
             if self.opts.generate_descriptions:
-                aTag['href'] = 'book_%d.html' % (int(float(book['id'])))
+                aTag['href'] = 'book_{}.html'.format(int(float(book['id'])))
 
             # Generate the title from the template
             args = self.generate_format_args(book)
@@ -2406,7 +2406,7 @@ class CatalogBuilder:
 
             aTag = soup.new_tag('a')
             if self.opts.generate_descriptions:
-                aTag['href'] = 'book_%d.html' % (int(float(book['id'])))
+                aTag['href'] = 'book_{}.html'.format(int(float(book['id'])))
             # Use series, series index if avail else just title
             # aTag.insert(0,'%d. %s · %s' % (book['series_index'],escape(book['title']), ' & '.join(book['authors'])))
 
@@ -2566,7 +2566,7 @@ class CatalogBuilder:
             # Link to book
             aTag = soup.new_tag('a')
             if self.opts.generate_descriptions:
-                aTag['href'] = 'book_%d.html' % (int(float(book['id'])))
+                aTag['href'] = 'book_{}.html'.format(int(float(book['id'])))
 
             # Generate the title from the template
             args = self.generate_format_args(book)
@@ -2728,7 +2728,7 @@ class CatalogBuilder:
         _soup = BeautifulSoup('<html>', selfClosingTags=['img'])
         thumb = _soup.new_tag('img')
         if book.get('cover'):
-            thumb['src'] = '../images/thumbnail_%d.jpg' % int(book['id'])
+            thumb['src'] = '../images/thumbnail_{}.jpg'.format(int(book['id']))
         else:
             thumb['src'] = '../images/thumbnail_default.jpg'
         thumb['alt'] = 'cover thumbnail'
@@ -2766,7 +2766,7 @@ class CatalogBuilder:
         btc = 0
         # Insert the title anchor for inbound links
         aTag = soup.new_tag('a')
-        aTag['id'] = 'book%d' % int(book['id'])
+        aTag['id'] = 'book{}'.format(int(book['id']))
         divTag = soup.new_tag('div')
         divTag.insert(0, aTag)
         body.insert(btc, divTag)
@@ -2839,7 +2839,7 @@ class CatalogBuilder:
             soup = self.generate_html_description_header(title)
 
             # Write the book entry to content_dir
-            with open('%s/book_%d.html' % (self.content_dir, int(title['id'])), 'wb') as outfile:
+            with open('{}/book_{}.html'.format(self.content_dir, int(title['id'])), 'wb') as outfile:
                 outfile.write(prettify(soup).encode('utf-8'))
 
     def generate_html_empty_header(self, title):
@@ -2990,7 +2990,7 @@ class CatalogBuilder:
                 makeelement('content', navPointTag, src='content/ByDateAdded.html')
             elif self.opts.generate_descriptions:
                 # Descriptions only
-                makeelement('content', navPointTag, src='content/book_%d.html' % int(self.books_by_description[0]['id']))
+                makeelement('content', navPointTag, src='content/book_{}.html'.format(int(self.books_by_description[0]['id'])))
 
     def generate_ncx_section_header(self, section_id, section_header, content_src):
         root = self.ncx_root
@@ -3038,7 +3038,8 @@ class CatalogBuilder:
         section_header = f'{tocTitle} [{len(self.books_by_description)}]'
         if self.generate_for_kindle_mobi:
             section_header = tocTitle
-        navPointTag = self.generate_ncx_section_header('bydescription-ID', section_header, 'content/book_%d.html' % int(self.books_by_description[0]['id']))
+        navPointTag = self.generate_ncx_section_header(
+            'bydescription-ID', section_header, 'content/book_{}.html'.format(int(self.books_by_description[0]['id'])))
 
         self.update_progress_full_step(_('NCX for descriptions'))
 
@@ -3047,7 +3048,7 @@ class CatalogBuilder:
         # Loop over the titles
 
         for book in self.books_by_description:
-            sec_id = 'book%dID' % int(book['id'])
+            sec_id = 'book{}ID'.format(int(book['id']))
             if book['series']:
                 series_index = str(book['series_index'])
                 if series_index.endswith('.0'):
@@ -3073,7 +3074,7 @@ class CatalogBuilder:
                     # Include Author for non-Kindle
                     sec_text = self.format_ncx_text('{} · {}'.format(book['title'], book['author']), dest='title')
 
-            content_src='content/book_%d.html#book%d' % (int(book['id']), int(book['id']))
+            content_src='content/book_{}.html#book{}'.format(int(book['id']), int(book['id']))
             cm_tags = {}
 
             if book['date']:
@@ -3677,7 +3678,7 @@ class CatalogBuilder:
 
         for book in self.books_by_description:
             # manifest
-            manifest_item('book%d' % int(book['id']), 'content/book_%d.html' % int(book['id']), 'application/xhtml+xml', add_to_spine=True)
+            manifest_item('book{}'.format(int(book['id'])), 'content/book_{}.html'.format(int(book['id'])), 'application/xhtml+xml', add_to_spine=True)
 
         # Guide
         if self.generate_for_kindle_mobi:
@@ -3922,12 +3923,12 @@ class CatalogBuilder:
                 (_('Thumbnail'), i, len(self.books_by_title)),
                  i / float(len(self.books_by_title)))
 
-            thumb_file = 'thumbnail_%d.jpg' % int(title['id'])
+            thumb_file = 'thumbnail_{}.jpg'.format(int(title['id']))
             thumb_generated = True
             valid_cover = True
             try:
                 self.generate_thumbnail(title, image_dir, thumb_file)
-                thumbs.append('thumbnail_%d.jpg' % int(title['id']))
+                thumbs.append('thumbnail_{}.jpg'.format(int(title['id'])))
             except:
                 if 'cover' in title and os.path.exists(title['cover']):
                     valid_cover = False
diff --git a/src/calibre/library/database2.py b/src/calibre/library/database2.py
index 37b4c3521d..497de92981 100644
--- a/src/calibre/library/database2.py
+++ b/src/calibre/library/database2.py
@@ -90,7 +90,7 @@ class LibraryDatabase2(LibraryDatabase, SchemaUpgrade, CustomColumns):
 
     @user_version.setter
     def user_version(self, val):
-        self.conn.execute('pragma user_version=%d'%int(val))
+        self.conn.execute(f'pragma user_version={int(val)}')
         self.conn.commit()
 
     @property
diff --git a/src/calibre/srv/http_response.py b/src/calibre/srv/http_response.py
index 0e2a97e1b5..8d5d672d08 100644
--- a/src/calibre/srv/http_response.py
+++ b/src/calibre/srv/http_response.py
@@ -506,7 +506,7 @@ class HTTPConnection(HTTPRequest):
         outheaders.set('Server', f'calibre {__version__}', replace_all=True)
         keep_alive = not self.close_after_response and self.opts.timeout > 0
         if keep_alive:
-            outheaders.set('Keep-Alive', 'timeout=%d' % int(self.opts.timeout))
+            outheaders.set('Keep-Alive', f'timeout={int(self.opts.timeout)}')
         if 'Connection' not in outheaders:
             if self.response_protocol is HTTP11:
                 if self.close_after_response:
diff --git a/src/calibre/web/feeds/recipes/collection.py b/src/calibre/web/feeds/recipes/collection.py
index 1a4921d5ac..b47eea443a 100644
--- a/src/calibre/web/feeds/recipes/collection.py
+++ b/src/calibre/web/feeds/recipes/collection.py
@@ -574,7 +574,7 @@ class SchedulerConfig:
                     if urn.startswith('recipe_'):
                         urn = 'builtin:'+urn[7:]
                     else:
-                        urn = 'custom:%d'%int(urn)
+                        urn = f'custom:{int(urn)}'
                     try:
                         username, password = c[k]
                     except:
@@ -596,14 +596,14 @@ class SchedulerConfig:
             urn = 'builtin:'+r['id'][7:]
         elif not r['builtin']:
             try:
-                urn = 'custom:%d'%int(r['id'])
+                urn = 'custom:{}'.format(int(r['id']))
             except:
                 return
         schedule = r['schedule']
         typ = 'interval'
         if schedule > 1e5:
             typ = 'day/time'
-            raw = '%d'%int(schedule)
+            raw = str(int(schedule))
             day = int(raw[0]) - 1
             hour = int(raw[2:4]) - 1
             minute = int(raw[-2:]) - 1
diff --git a/src/calibre/web/feeds/templates.py b/src/calibre/web/feeds/templates.py
index 15a9730435..7e484b5f88 100644
--- a/src/calibre/web/feeds/templates.py
+++ b/src/calibre/web/feeds/templates.py
@@ -313,7 +313,7 @@ class TouchscreenFeedTemplate(Template):
         if f > 0:
             link = A(attrs('feed_link'),
                      trim_title(feeds[f-1].title),
-                     href='../feed_%d/index.html' % int(f-1))
+                     href=f'../feed_{int(f-1)}/index.html')
         navbar_tr.append(TD(attrs('feed_prev'),link))
 
         # Up to Sections
@@ -325,7 +325,7 @@ class TouchscreenFeedTemplate(Template):
         if f < len(feeds)-1:
             link = A(attrs('feed_link'),
                      trim_title(feeds[f+1].title),
-                     href='../feed_%d/index.html' % int(f+1))
+                     href=f'../feed_{int(f+1)}/index.html')
         navbar_tr.append(TD(attrs('feed_next'),link))
         navbar_t.append(navbar_tr)
         top_navbar = navbar_t