diff --git a/lib/modules/platform/default-scm.spec.ts b/lib/modules/platform/default-scm.spec.ts
index 2f97a3c4ef..d7a7995bc9 100644
--- a/lib/modules/platform/default-scm.spec.ts
+++ b/lib/modules/platform/default-scm.spec.ts
@@ -45,7 +45,7 @@ describe('modules/platform/default-scm', () => {
 
   it('delegate isBranchModified to util/git', async () => {
     git.isBranchModified.mockResolvedValueOnce(true);
-    await defaultGitScm.isBranchModified('branchName');
+    await defaultGitScm.isBranchModified('branchName', 'main');
     expect(git.isBranchModified).toHaveBeenCalledTimes(1);
   });
 
diff --git a/lib/modules/platform/default-scm.ts b/lib/modules/platform/default-scm.ts
index 92ceef5421..c105a0bd16 100644
--- a/lib/modules/platform/default-scm.ts
+++ b/lib/modules/platform/default-scm.ts
@@ -27,8 +27,8 @@ export class DefaultGitScm implements PlatformScm {
     return git.isBranchConflicted(baseBranch, branch);
   }
 
-  isBranchModified(branchName: string): Promise<boolean> {
-    return git.isBranchModified(branchName);
+  isBranchModified(branchName: string, baseBranch?: string): Promise<boolean> {
+    return git.isBranchModified(branchName, baseBranch);
   }
 
   getFileList(): Promise<string[]> {
diff --git a/lib/modules/platform/types.ts b/lib/modules/platform/types.ts
index ca98ae3337..fb3ac95387 100644
--- a/lib/modules/platform/types.ts
+++ b/lib/modules/platform/types.ts
@@ -233,7 +233,7 @@ export interface Platform {
 
 export interface PlatformScm {
   isBranchBehindBase(branchName: string, baseBranch: string): Promise<boolean>;
-  isBranchModified(branchName: string): Promise<boolean>;
+  isBranchModified(branchName: string, baseBranch?: string): Promise<boolean>;
   isBranchConflicted(baseBranch: string, branch: string): Promise<boolean>;
   branchExists(branchName: string): Promise<boolean>;
   getBranchCommit(branchName: string): Promise<CommitSha | null>;
diff --git a/lib/util/git/index.spec.ts b/lib/util/git/index.spec.ts
index 3902d862a4..a8d8e426db 100644
--- a/lib/util/git/index.spec.ts
+++ b/lib/util/git/index.spec.ts
@@ -77,6 +77,20 @@ describe('util/git/index', () => {
     await repo.addConfig('user.email', 'custom@example.com');
     await repo.commit('custom message');
 
+    await repo.checkoutBranch('renovate/multiple_commits', defaultBranch);
+    await fs.writeFile(base.path + '/commit1', 'commit1');
+    await repo.add(['commit1']);
+    await repo.addConfig('user.email', 'author1@example.com');
+    await repo.commit('commit1 message');
+    await fs.writeFile(base.path + '/commit2', 'commit2');
+    await repo.add(['commit2']);
+    await repo.addConfig('user.email', 'author2@example.com');
+    await repo.commit('commit2 message');
+    await fs.writeFile(base.path + '/commit3', 'commit3');
+    await repo.add(['commit3']);
+    await repo.addConfig('user.email', 'author1@example.com');
+    await repo.commit('commit3 message');
+
     await repo.checkoutBranch('renovate/nested_files', defaultBranch);
     await fs.mkdirp(base.path + '/bin/');
     await fs.writeFile(base.path + '/bin/nested', 'nested');
@@ -275,11 +289,16 @@ describe('util/git/index', () => {
 
     it('should return false when branch is not found', async () => {
       expect(await git.isBranchModified('renovate/not_found')).toBeFalse();
+      expect(
+        await git.isBranchModified('renovate/not_found', defaultBranch)
+      ).toBeFalse();
     });
 
     it('should return false when author matches', async () => {
       expect(await git.isBranchModified('renovate/future_branch')).toBeFalse();
-      expect(await git.isBranchModified('renovate/future_branch')).toBeFalse();
+      expect(
+        await git.isBranchModified('renovate/future_branch', defaultBranch)
+      ).toBeFalse();
     });
 
     it('should return false when author is ignored', async () => {
@@ -287,15 +306,33 @@ describe('util/git/index', () => {
         gitIgnoredAuthors: ['custom@example.com'],
       });
       expect(await git.isBranchModified('renovate/custom_author')).toBeFalse();
+      expect(
+        await git.isBranchModified('renovate/custom_author', defaultBranch)
+      ).toBeFalse();
     });
 
     it('should return true when custom author is unknown', async () => {
       expect(await git.isBranchModified('renovate/custom_author')).toBeTrue();
+      expect(
+        await git.isBranchModified('renovate/custom_author', defaultBranch)
+      ).toBeTrue();
+    });
+
+    it('should return true if any commit is modified', async () => {
+      git.setUserRepoConfig({
+        gitIgnoredAuthors: ['author1@example.com'],
+      });
+      expect(
+        await git.isBranchModified('renovate/multiple_commits', defaultBranch)
+      ).toBeTrue();
     });
 
     it('should return value stored in modifiedCacheResult', async () => {
       modifiedCache.getCachedModifiedResult.mockReturnValue(true);
       expect(await git.isBranchModified('renovate/future_branch')).toBeTrue();
+      expect(
+        await git.isBranchModified('renovate/future_branch', defaultBranch)
+      ).toBeTrue();
     });
   });
 
diff --git a/lib/util/git/index.ts b/lib/util/git/index.ts
index c919e559ef..587eef39d4 100644
--- a/lib/util/git/index.ts
+++ b/lib/util/git/index.ts
@@ -616,7 +616,10 @@ export async function isBranchBehindBase(
   }
 }
 
-export async function isBranchModified(branchName: string): Promise<boolean> {
+export async function isBranchModified(
+  branchName: string,
+  baseBranch?: string
+): Promise<boolean> {
   if (!branchExists(branchName)) {
     logger.debug('branch.isModified(): no cache');
     return false;
@@ -636,21 +639,49 @@ export async function isBranchModified(branchName: string): Promise<boolean> {
     return isModified;
   }
 
-  logger.debug('branch.isModified(): using git to calculate');
-
   await syncGit();
-  // Retrieve the author of the most recent commit
-  let lastAuthor: string | undefined;
+  // Retrieve the commit authors
+  let branchAuthors: string[] = [];
   try {
-    lastAuthor = (
-      await git.raw([
-        'log',
-        '-1',
-        '--pretty=format:%ae',
-        `origin/${branchName}`,
-        '--',
-      ])
-    ).trim();
+    if (baseBranch) {
+      logger.debug(
+        `branch.isModified(): using git to calculate authors between ${branchName} and ${baseBranch}`
+      );
+      branchAuthors = [
+        ...new Set(
+          (
+            await git.raw([
+              'log',
+              '--pretty=format:%ae',
+              `origin/${branchName}..origin/${baseBranch}`,
+              '--',
+            ])
+          )
+            .trim()
+            .split(newlineRegex)
+        ),
+      ];
+      logger.debug(`Git authors in branch: ${branchAuthors.join(', ')}`);
+    } else {
+      logger.debug(
+        `branch.isModified(): checking last author of ${branchName}`
+      );
+      branchAuthors = [
+        ...new Set(
+          (
+            await git.raw([
+              'log',
+              '-1',
+              '--pretty=format:%ae',
+              `origin/${branchName}`,
+              '--',
+            ])
+          )
+            .trim()
+            .split(newlineRegex)
+        ),
+      ];
+    }
   } catch (err) /* istanbul ignore next */ {
     if (err.message?.includes('fatal: bad revision')) {
       logger.debug(
@@ -659,26 +690,20 @@ export async function isBranchModified(branchName: string): Promise<boolean> {
       );
       throw new Error(REPOSITORY_CHANGED);
     }
-    logger.warn({ err }, 'Error checking last author for isBranchModified');
+    logger.warn({ err }, 'Error retrieving git authors for isBranchModified');
   }
   const { gitAuthorEmail } = config;
-  if (
-    lastAuthor === gitAuthorEmail ||
-    config.ignoredAuthors.some((ignoredAuthor) => lastAuthor === ignoredAuthor)
-  ) {
-    // author matches - branch has not been modified
-    logger.debug('branch.isModified() = false');
-    config.branchIsModified[branchName] = false;
-    setCachedModifiedResult(branchName, false);
-    return false;
+  let branchIsModified = false;
+  for (const author of branchAuthors) {
+    if (author !== gitAuthorEmail && !config.ignoredAuthors.includes(author)) {
+      logger.debug(`branch.isModified=true due to this git author: ${author}`);
+      branchIsModified = true;
+    }
   }
-  logger.debug(
-    { branchName, lastAuthor, gitAuthorEmail },
-    'branch.isModified() = true'
-  );
-  config.branchIsModified[branchName] = true;
-  setCachedModifiedResult(branchName, true);
-  return true;
+  logger.debug(`branch.isModified() = ${branchIsModified}`);
+  config.branchIsModified[branchName] = branchIsModified;
+  setCachedModifiedResult(branchName, branchIsModified);
+  return branchIsModified;
 }
 
 export async function isBranchConflicted(
diff --git a/lib/workers/repository/config-migration/branch/rebase.ts b/lib/workers/repository/config-migration/branch/rebase.ts
index eb082c893a..4872685cb7 100644
--- a/lib/workers/repository/config-migration/branch/rebase.ts
+++ b/lib/workers/repository/config-migration/branch/rebase.ts
@@ -16,7 +16,7 @@ export async function rebaseMigrationBranch(
 ): Promise<string | null> {
   logger.debug('Checking if migration branch needs rebasing');
   const branchName = getMigrationBranchName(config);
-  if (await scm.isBranchModified(branchName)) {
+  if (await scm.isBranchModified(branchName, config.baseBranch)) {
     logger.debug('Migration branch has been edited and cannot be rebased');
     return null;
   }
diff --git a/lib/workers/repository/update/branch/index.ts b/lib/workers/repository/update/branch/index.ts
index a78d2f1fca..c3c381f883 100644
--- a/lib/workers/repository/update/branch/index.ts
+++ b/lib/workers/repository/update/branch/index.ts
@@ -242,7 +242,10 @@ export async function processBranch(
       }
 
       logger.debug('Checking if PR has been edited');
-      const branchIsModified = await scm.isBranchModified(config.branchName);
+      const branchIsModified = await scm.isBranchModified(
+        config.branchName,
+        config.baseBranch
+      );
       if (branchPr) {
         logger.debug('Found existing branch PR');
         if (branchPr.state !== 'open') {
diff --git a/lib/workers/repository/update/branch/reuse.ts b/lib/workers/repository/update/branch/reuse.ts
index d2b3a7b1ac..4abfbccd2a 100644
--- a/lib/workers/repository/update/branch/reuse.ts
+++ b/lib/workers/repository/update/branch/reuse.ts
@@ -29,7 +29,7 @@ export async function shouldReuseExistingBranch(
     if (await scm.isBranchBehindBase(branchName, baseBranch)) {
       logger.debug(`Branch is behind base branch and needs rebasing`);
       // We can rebase the branch only if no PR or PR can be rebased
-      if (await scm.isBranchModified(branchName)) {
+      if (await scm.isBranchModified(branchName, baseBranch)) {
         logger.debug('Cannot rebase branch as it has been modified');
         result.reuseExistingBranch = true;
         result.isModified = true;
@@ -50,7 +50,7 @@ export async function shouldReuseExistingBranch(
   if (result.isConflicted) {
     logger.debug('Branch is conflicted');
 
-    if ((await scm.isBranchModified(branchName)) === false) {
+    if ((await scm.isBranchModified(branchName, baseBranch)) === false) {
       logger.debug(`Branch is not mergeable and needs rebasing`);
       if (config.rebaseWhen === 'never') {
         logger.debug('Rebasing disabled by config');
diff --git a/lib/workers/repository/update/pr/automerge.ts b/lib/workers/repository/update/pr/automerge.ts
index 2e9465ea97..b9baebcf28 100644
--- a/lib/workers/repository/update/pr/automerge.ts
+++ b/lib/workers/repository/update/pr/automerge.ts
@@ -82,7 +82,7 @@ export async function checkAutoMerge(
     };
   }
   // Check if it's been touched
-  if (await scm.isBranchModified(branchName)) {
+  if (await scm.isBranchModified(branchName, config.baseBranch)) {
     logger.debug('PR is ready for automerge but has been modified');
     return {
       automerged: false,