diff --git a/cypress/integration/rendering/gantt.spec.js b/cypress/integration/rendering/gantt.spec.js
index ec33e01aa..979c27540 100644
--- a/cypress/integration/rendering/gantt.spec.js
+++ b/cypress/integration/rendering/gantt.spec.js
@@ -661,6 +661,35 @@ describe('Gantt diagram', () => {
     );
   });
 
+  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 0695544ce..dd4824d6b 100644
--- a/packages/mermaid/src/diagrams/gantt/ganttRenderer.js
+++ b/packages/mermaid/src/diagrams/gantt/ganttRenderer.js
@@ -554,14 +554,12 @@ export const draw = function (text, id, version, diagObj) {
       return;
     }
 
-    const normalizedExcludes = excludes.map((d) => dayjs(d).format('YYYY-MM-DD'));
-    const normalizedIncludes = includes.map((d) => dayjs(d).format('YYYY-MM-DD'));
+    const dateFormat = diagObj.db.getDateFormat();
     const excludeRanges = [];
     let range = null;
     let d = dayjs(minTime);
     while (d.valueOf() <= maxTime) {
-      const dStr = d.format('YYYY-MM-DD');
-      if (normalizedExcludes.includes(dStr) && !normalizedIncludes.includes(dStr)) {
+      if (diagObj.db.isInvalidDate(d, dateFormat, excludes, includes)) {
         if (!range) {
           range = {
             start: d,