diff --git a/cypress/integration/rendering/gantt.spec.js b/cypress/integration/rendering/gantt.spec.js
index 2cc67918c..ec33e01aa 100644
--- a/cypress/integration/rendering/gantt.spec.js
+++ b/cypress/integration/rendering/gantt.spec.js
@@ -647,6 +647,20 @@ 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 when there's a semicolon in the title", () => {
     imgSnapshotTest(
       `
diff --git a/packages/mermaid/src/diagrams/gantt/ganttRenderer.js b/packages/mermaid/src/diagrams/gantt/ganttRenderer.js
index f5c8c2e38..0695544ce 100644
--- a/packages/mermaid/src/diagrams/gantt/ganttRenderer.js
+++ b/packages/mermaid/src/diagrams/gantt/ganttRenderer.js
@@ -554,12 +554,14 @@ export const draw = function (text, id, version, diagObj) {
       return;
     }
 
-    const dateFormat = diagObj.db.getDateFormat();
+    const normalizedExcludes = excludes.map((d) => dayjs(d).format('YYYY-MM-DD'));
+    const normalizedIncludes = includes.map((d) => dayjs(d).format('YYYY-MM-DD'));
     const excludeRanges = [];
     let range = null;
     let d = dayjs(minTime);
     while (d.valueOf() <= maxTime) {
-      if (diagObj.db.isInvalidDate(d, dateFormat, excludes, includes)) {
+      const dStr = d.format('YYYY-MM-DD');
+      if (normalizedExcludes.includes(dStr) && !normalizedIncludes.includes(dStr)) {
         if (!range) {
           range = {
             start: d,
@@ -581,17 +583,11 @@ 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 (