diff --git a/README.md b/README.md
index 1631040..183717c 100644
--- a/README.md
+++ b/README.md
@@ -83,6 +83,10 @@ $ git clone ...
 
 $ phpstan-baseline-analyze *phpstan-baseline.neon --json > now.json
 
+# To use baseline file modification time as the analysis date instead of "now"
+# Best used together with `git restore-mtime *phpstan-baseline.neon`
+$ phpstan-baseline-analyze *phpstan-baseline.neon --json --mtime > now.json
+
 $ git checkout `git rev-list -n 1 --before="1 week ago" HEAD`
 $ phpstan-baseline-analyze '*phpstan-baseline.neon' --json > 1-week-ago.json
 
@@ -92,6 +96,8 @@ $ phpstan-baseline-analyze '*phpstan-baseline.neon' --json > 2-weeks-ago.json
 $ php phpstan-baseline-graph '*.json' > result.html
 ```
 
+See [git-tools](https://github.com/MestreLion/git-tools) for details on `git restore-mtime`
+
 ![PHPStan baseline analysis graph](https://github.com/staabm/phpstan-baseline-analysis/assets/120441/ea5abe25-21e8-43f2-9118-0967a75517c6)
 
 
diff --git a/bin/phpstan-baseline-analyze.php b/bin/phpstan-baseline-analyze.php
index f5c56a8..0fc8517 100644
--- a/bin/phpstan-baseline-analyze.php
+++ b/bin/phpstan-baseline-analyze.php
@@ -35,9 +35,14 @@
 
 
 $format = ResultPrinter::FORMAT_TEXT;
+$useFileMtime = false;
 if (in_array('--json', $argv)) {
     $format = ResultPrinter::FORMAT_JSON;
 }
 
-$exitCode = $app->start($argv[1], $format);
+if (in_array('--mtime', $argv)) {
+    $useFileMtime = true;
+}
+
+$exitCode = $app->start($argv[1], $format, $useFileMtime);
 exit($exitCode);
diff --git a/lib/AnalyzeApplication.php b/lib/AnalyzeApplication.php
index deb39f9..b803c21 100644
--- a/lib/AnalyzeApplication.php
+++ b/lib/AnalyzeApplication.php
@@ -24,7 +24,7 @@ final class AnalyzeApplication
      *
      * @api
      */
-    public function start(string $glob, string $format): int
+    public function start(string $glob, string $format, bool $useFileMtime = false): int
     {
         $printer = new ResultPrinter();
         $baselines = BaselineFinder::forGlob($glob);
@@ -36,6 +36,7 @@ public function start(string $glob, string $format): int
             $isLast = $i == $numBaselines - 1;
 
             $analyzer = new BaselineAnalyzer($baseline);
+            $analyzer->useFileMtime($useFileMtime);
             $result = $analyzer->analyze();
 
             if ($format == ResultPrinter::FORMAT_JSON) {
diff --git a/lib/BaselineAnalyzer.php b/lib/BaselineAnalyzer.php
index 31a5bd7..4e9cce4 100644
--- a/lib/BaselineAnalyzer.php
+++ b/lib/BaselineAnalyzer.php
@@ -3,7 +3,7 @@
 namespace staabm\PHPStanBaselineAnalysis;
 
 use Safe\DateTimeImmutable;
-use function Safe\preg_match;
+use function Safe\filemtime;
 
 final class BaselineAnalyzer
 {
@@ -32,16 +32,26 @@ final class BaselineAnalyzer
      * @var Baseline
      */
     private $baseline;
+    private bool $fileMtime;
 
     public function __construct(Baseline $baseline)
     {
         $this->baseline = $baseline;
     }
 
+    public function useFileMtime(bool $useFileMtime)
+    {
+        $this->fileMtime = $useFileMtime;
+    }
+
     public function analyze(): AnalyzerResult
     {
         $result = new AnalyzerResult();
-        $result->referenceDate = new DateTimeImmutable();
+        if ($this->fileMtime) {
+            $result->referenceDate = DateTimeImmutable::createFromFormat("U", (string)filemtime($this->baseline->getFilePath()));
+        } else {
+            $result->referenceDate = new DateTimeImmutable();
+        }
 
         /**
          * @var BaselineError $baselineError
diff --git a/lib/GraphTemplate.php b/lib/GraphTemplate.php
index e86bc76..7e8d6b7 100644
--- a/lib/GraphTemplate.php
+++ b/lib/GraphTemplate.php
@@ -103,6 +103,7 @@ public function render(Iterator $it):string {
         }
 
         foreach ($dataByDates as $baselinePath => $dataByDate) {
+            ksort($dataByDate);
             foreach ($dataByDate as $date => $data) {
                 $dates[$baselinePath][] = 'new Date(' . $date . ' * 1000).toLocaleDateString("de-DE")';
                 $splines[$baselinePath][0]['data'][] = $data[0];
diff --git a/tests/AnalyzeApplicationTest.php b/tests/AnalyzeApplicationTest.php
index 10e4700..44b8989 100644
--- a/tests/AnalyzeApplicationTest.php
+++ b/tests/AnalyzeApplicationTest.php
@@ -2,13 +2,17 @@
 
 namespace staabm\PHPStanBaselineAnalysis\Tests;
 
+use Safe\DateTimeImmutable;
 use staabm\PHPStanBaselineAnalysis\AnalyzeApplication;
 use staabm\PHPStanBaselineAnalysis\ResultPrinter;
+
+use function Safe\filemtime;
 use function Safe\json_encode;
+use function Safe\ob_start;
 
 class AnalyzeApplicationTest extends BaseTestCase
 {
-    function testTextPrinting():void
+    function testTextPrintingWithCurrentTime():void
     {
         $app = new AnalyzeApplication();
 
@@ -33,6 +37,37 @@ function testTextPrinting():void
   Native-Return-Type-Coverage: 4
   Unused-Symbols: 3
 
+PHP;
+
+        $this->assertSame($expected, $rendered);
+        $this->assertSame(0, $exitCode);
+    }
+
+    function testTextPrintingWithFileModificationTime():void
+    {
+        $app = new AnalyzeApplication();
+
+        ob_start();
+        $exitCode = $app->start(__DIR__ . '/fixtures/all-in.neon', ResultPrinter::FORMAT_TEXT, true);
+        $rendered = ob_get_clean();
+
+        $rendered = str_replace(__DIR__, '', $rendered);
+
+        $expectedDate = DateTimeImmutable::createFromFormat("U", (string) filemtime(__DIR__ . '/fixtures/all-in.neon'))->format(ResultPrinter::DATE_FORMAT);
+        $expected = <<<PHP
+Analyzing /fixtures/all-in.neon
+  Date: {$expectedDate}
+  Overall-Errors: 41
+  Classes-Cognitive-Complexity: 70
+  Deprecations: 2
+  Invalid-Phpdocs: 5
+  Unknown-Types: 1
+  Anonymous-Variables: 4
+  Native-Property-Type-Coverage: 1
+  Native-Param-Type-Coverage: 27
+  Native-Return-Type-Coverage: 4
+  Unused-Symbols: 3
+
 PHP;
 
         $this->assertSame($expected, $rendered);