diff --git a/packages/trpc/server/routers/viewer/slots/util.test.ts b/packages/trpc/server/routers/viewer/slots/util.test.ts
index b3ede3d45e472c..5db75874a5ec30 100644
--- a/packages/trpc/server/routers/viewer/slots/util.test.ts
+++ b/packages/trpc/server/routers/viewer/slots/util.test.ts
@@ -1,7 +1,10 @@
 import { describe, expect, it } from "vitest";
 
 import type { GetAvailabilityUser } from "@calcom/core/getUserAvailability";
+import dayjs from "@calcom/dayjs";
+import type { EventBusyDate } from "@calcom/types/Calendar";
 
+import { checkIfIsAvailable } from "./util";
 import { getUsersWithCredentialsConsideringContactOwner } from "./util";
 
 describe("getUsersWithCredentialsConsideringContactOwner", () => {
@@ -88,3 +91,163 @@ describe("getUsersWithCredentialsConsideringContactOwner", () => {
     ]);
   });
 });
+
+describe("checkIfIsAvailable", () => {
+  const createTestData = (time: string) => ({
+    time: dayjs(time),
+    eventLength: 30,
+    busy: [] as EventBusyDate[],
+  });
+
+  describe("currentSeats handling", () => {
+    it("should return true if slot exists in currentSeats", () => {
+      const currentSeats: CurrentSeats = [
+        {
+          uid: "123",
+          startTime: dayjs.utc("2023-01-01T09:00:00Z").toDate(),
+          _count: { attendees: 1 },
+        },
+      ];
+
+      const result = checkIfIsAvailable({
+        ...createTestData("2023-01-01T09:00:00Z"),
+        currentSeats,
+      });
+
+      expect(result).toBe(true);
+    });
+  });
+
+  describe("busy time overlap scenarios", () => {
+    it("should return true when no busy periods", () => {
+      const result = checkIfIsAvailable(createTestData("2023-01-01T09:00:00Z"));
+      expect(result).toBe(true);
+    });
+
+    it("should return true when busy period ends before slot starts", () => {
+      const result = checkIfIsAvailable({
+        ...createTestData("2023-01-01T09:00:00Z"),
+        busy: [
+          {
+            start: dayjs.utc("2023-01-01T08:00:00Z").toDate(),
+            end: dayjs.utc("2023-01-01T08:30:00Z").toDate(),
+          },
+        ],
+      });
+      expect(result).toBe(true);
+    });
+
+    it("should return true when busy period starts after slot ends", () => {
+      const result = checkIfIsAvailable({
+        ...createTestData("2023-01-01T09:00:00Z"),
+        busy: [
+          {
+            start: dayjs.utc("2023-01-01T10:00:00Z").toDate(),
+            end: dayjs.utc("2023-01-01T10:30:00Z").toDate(),
+          },
+        ],
+      });
+      expect(result).toBe(true);
+    });
+
+    it("should return false when slot start falls within busy period", () => {
+      const result = checkIfIsAvailable({
+        ...createTestData("2023-01-01T09:15:00Z"),
+        busy: [
+          {
+            start: dayjs.utc("2023-01-01T09:00:00Z").toDate(),
+            end: dayjs.utc("2023-01-01T09:30:00Z").toDate(),
+          },
+        ],
+      });
+      expect(result).toBe(false);
+    });
+
+    it("should return false when slot end falls within busy period", () => {
+      const result = checkIfIsAvailable({
+        ...createTestData("2023-01-01T08:45:00Z"),
+        busy: [
+          {
+            start: dayjs.utc("2023-01-01T09:00:00Z").toDate(),
+            end: dayjs.utc("2023-01-01T09:30:00Z").toDate(),
+          },
+        ],
+      });
+      expect(result).toBe(false);
+    });
+
+    it("should return false when busy period is completely contained within slot", () => {
+      const result = checkIfIsAvailable({
+        ...createTestData("2023-01-01T09:00:00Z"),
+        eventLength: 60,
+        busy: [
+          {
+            start: dayjs.utc("2023-01-01T09:15:00Z").toDate(),
+            end: dayjs.utc("2023-01-01T09:45:00Z").toDate(),
+          },
+        ],
+      });
+      expect(result).toBe(false);
+    });
+
+    it("should return false when slot is completely contained within busy period", () => {
+      const result = checkIfIsAvailable({
+        ...createTestData("2023-01-01T09:15:00Z"),
+        busy: [
+          {
+            start: dayjs.utc("2023-01-01T09:00:00Z").toDate(),
+            end: dayjs.utc("2023-01-01T10:00:00Z").toDate(),
+          },
+        ],
+      });
+      expect(result).toBe(false);
+    });
+
+    it("should return true when multiple non-overlapping busy periods", () => {
+      const result = checkIfIsAvailable({
+        ...createTestData("2023-01-01T09:30:00Z"),
+        busy: [
+          {
+            start: dayjs.utc("2023-01-01T08:00:00Z").toDate(),
+            end: dayjs.utc("2023-01-01T09:00:00Z").toDate(),
+          },
+          {
+            start: dayjs.utc("2023-01-01T10:00:00Z").toDate(),
+            end: dayjs.utc("2023-01-01T11:00:00Z").toDate(),
+          },
+        ],
+      });
+      expect(result).toBe(true);
+    });
+
+    it("should return false if any busy period overlaps", () => {
+      const result = checkIfIsAvailable({
+        ...createTestData("2023-01-01T09:30:00Z"),
+        busy: [
+          {
+            start: dayjs.utc("2023-01-01T08:00:00Z").toDate(),
+            end: dayjs.utc("2023-01-01T09:00:00Z").toDate(),
+          },
+          {
+            start: dayjs.utc("2023-01-01T09:45:00Z").toDate(),
+            end: dayjs.utc("2023-01-01T10:00:00Z").toDate(),
+          },
+        ],
+      });
+      expect(result).toBe(false);
+    });
+
+    it("should handle exact boundary conditions", () => {
+      const result = checkIfIsAvailable({
+        ...createTestData("2023-01-01T09:30:00Z"),
+        busy: [
+          {
+            start: dayjs.utc("2023-01-01T09:00:00Z").toDate(),
+            end: dayjs.utc("2023-01-01T09:30:00Z").toDate(),
+          },
+        ],
+      });
+      expect(result).toBe(true);
+    });
+  });
+});
diff --git a/packages/trpc/server/routers/viewer/slots/util.ts b/packages/trpc/server/routers/viewer/slots/util.ts
index d9dfff3a5a897c..7d06464979465e 100644
--- a/packages/trpc/server/routers/viewer/slots/util.ts
+++ b/packages/trpc/server/routers/viewer/slots/util.ts
@@ -62,33 +62,38 @@ export const checkIfIsAvailable = ({
     return true;
   }
 
-  const slotEndTime = time.add(eventLength, "minutes").utc();
-  const slotStartTime = time.utc();
+  const slotStartDate = time.utc().toDate();
+  const slotEndDate = time.add(eventLength, "minutes").utc().toDate();
 
   return busy.every((busyTime) => {
-    const startTime = dayjs.utc(busyTime.start).utc();
-    const endTime = dayjs.utc(busyTime.end);
+    const busyStartDate = dayjs.utc(busyTime.start).toDate();
+    const busyEndDate = dayjs.utc(busyTime.end).toDate();
 
-    if (endTime.isBefore(slotStartTime) || startTime.isAfter(slotEndTime)) {
+    // First check if there's any overlap at all
+    // If busy period ends before slot starts or starts after slot ends, there's no overlap
+    if (busyEndDate <= slotStartDate || busyStartDate >= slotEndDate) {
       return true;
     }
 
-    if (slotStartTime.isBetween(startTime, endTime, null, "[)")) {
-      return false;
-    } else if (slotEndTime.isBetween(startTime, endTime, null, "(]")) {
+    // Now check all possible overlap scenarios:
+
+    // 1. Slot start falls within busy period (inclusive start, exclusive end)
+    if (slotStartDate >= busyStartDate && slotStartDate < busyEndDate) {
       return false;
     }
 
-    // Check if start times are the same
-    if (time.utc().isBetween(startTime, endTime, null, "[)")) {
+    // 2. Slot end falls within busy period (exclusive start, inclusive end)
+    if (slotEndDate > busyStartDate && slotEndDate <= busyEndDate) {
       return false;
     }
-    // Check if slot end time is between start and end time
-    else if (slotEndTime.isBetween(startTime, endTime)) {
+
+    // 3. Busy period completely contained within slot
+    if (busyStartDate >= slotStartDate && busyEndDate <= slotEndDate) {
       return false;
     }
-    // Check if startTime is between slot
-    else if (startTime.isBetween(time, slotEndTime)) {
+
+    // 4. Slot completely contained within busy period
+    if (busyStartDate <= slotStartDate && busyEndDate >= slotEndDate) {
       return false;
     }