diff --git a/.changeset/fuzzy-pears-cough.md b/.changeset/fuzzy-pears-cough.md
new file mode 100644
index 000000000..6ed777506
--- /dev/null
+++ b/.changeset/fuzzy-pears-cough.md
@@ -0,0 +1,5 @@
+---
+'mermaid': patch
+---
+
+fix: handle exclude dates properly in Gantt charts when using dateFormat: 'YYYY-MM-DD HH:mm:ss'
diff --git a/cypress/integration/rendering/gantt.spec.js b/cypress/integration/rendering/gantt.spec.js
index 2cc67918c..979c27540 100644
--- a/cypress/integration/rendering/gantt.spec.js
+++ b/cypress/integration/rendering/gantt.spec.js
@@ -647,6 +647,49 @@ describe('Gantt diagram', () => {
     );
   });
 
+  it('should render a gantt diagram excluding a specific date in YYYY-MM-DD HH:mm:ss format', () => {
+    imgSnapshotTest(
+      `
+    gantt
+      dateFormat  YYYY-MM-DD HH:mm:ss
+      excludes    2025-07-07
+      section     Section
+      A task      :a1, 2025-07-04 20:30:30, 2025-07-08 10:30:30
+      Another task:after a1, 20h
+    `,
+      {}
+    );
+  });
+
+  it('should render a gantt diagram excluding saturday and sunday in YYYY-MM-DD HH:mm:ss format', () => {
+    imgSnapshotTest(
+      `
+        gantt
+      dateFormat  YYYY-MM-DD HH:mm:ss
+      excludes    weekends
+       weekend saturday
+      section     Section
+      A task      :a1, 2025-07-04 20:30:30, 2025-07-08 10:30:30
+      Another task:after a1, 20h
+    `,
+      {}
+    );
+  });
+  it('should render a gantt diagram excluding friday and saturday in YYYY-MM-DD HH:mm:ss format', () => {
+    imgSnapshotTest(
+      `
+        gantt
+      dateFormat  YYYY-MM-DD HH:mm:ss
+      excludes    weekends
+       weekend friday
+      section     Section
+      A task      :a1, 2025-07-04 20:30:30, 2025-07-08 10:30:30
+      Another task:after a1, 20h
+    `,
+      {}
+    );
+  });
+
   it("should render when there's a semicolon in the title", () => {
     imgSnapshotTest(
       `
diff --git a/packages/mermaid/src/diagrams/gantt/ganttDb.js b/packages/mermaid/src/diagrams/gantt/ganttDb.js
index 3ae55fb25..b2b5b0566 100644
--- a/packages/mermaid/src/diagrams/gantt/ganttDb.js
+++ b/packages/mermaid/src/diagrams/gantt/ganttDb.js
@@ -167,7 +167,10 @@ export const getTasks = function () {
 };
 
 export const isInvalidDate = function (date, dateFormat, excludes, includes) {
-  if (includes.includes(date.format(dateFormat.trim()))) {
+  const formattedDate = date.format(dateFormat.trim());
+  const dateOnly = date.format('YYYY-MM-DD');
+
+  if (includes.includes(formattedDate) || includes.includes(dateOnly)) {
     return false;
   }
   if (
@@ -180,7 +183,7 @@ export const isInvalidDate = function (date, dateFormat, excludes, includes) {
   if (excludes.includes(date.format('dddd').toLowerCase())) {
     return true;
   }
-  return excludes.includes(date.format(dateFormat.trim()));
+  return excludes.includes(formattedDate) || excludes.includes(dateOnly);
 };
 
 export const setWeekday = function (txt) {
diff --git a/packages/mermaid/src/diagrams/gantt/ganttRenderer.js b/packages/mermaid/src/diagrams/gantt/ganttRenderer.js
index f5c8c2e38..dd4824d6b 100644
--- a/packages/mermaid/src/diagrams/gantt/ganttRenderer.js
+++ b/packages/mermaid/src/diagrams/gantt/ganttRenderer.js
@@ -581,17 +581,11 @@ export const draw = function (text, id, version, diagObj) {
 
     rectangles
       .append('rect')
-      .attr('id', function (d) {
-        return 'exclude-' + d.start.format('YYYY-MM-DD');
-      })
-      .attr('x', function (d) {
-        return timeScale(d.start) + theSidePad;
-      })
+      .attr('id', (d) => 'exclude-' + d.start.format('YYYY-MM-DD'))
+      .attr('x', (d) => timeScale(d.start.startOf('day')) + theSidePad)
       .attr('y', conf.gridLineStartPadding)
-      .attr('width', function (d) {
-        const renderEnd = d.end.add(1, 'day');
-        return timeScale(renderEnd) - timeScale(d.start);
-      })
+      .attr('width', (d) => timeScale(d.end.endOf('day')) - timeScale(d.start.startOf('day')))
+
       .attr('height', h - theTopPad - conf.gridLineStartPadding)
       .attr('transform-origin', function (d, i) {
         return (