diff --git a/backend/routes/rentals.js b/backend/routes/rentals.js
index b3886b0..7fed6aa 100644
--- a/backend/routes/rentals.js
+++ b/backend/routes/rentals.js
@@ -273,37 +273,20 @@ router.post("/", authenticateToken, requireVerifiedEmail, async (req, res) => {
 
     // Check for overlapping rentals using datetime ranges
     // Note: "active" rentals are stored as "confirmed" with startDateTime in the past
+    // Two ranges [A,B] and [C,D] overlap if and only if A < D AND C < B
+    // Here: existing rental [existingStart, existingEnd], new rental [rentalStartDateTime, rentalEndDateTime]
+    // Overlap: existingStart < rentalEndDateTime AND rentalStartDateTime < existingEnd
     const overlappingRental = await Rental.findOne({
       where: {
         itemId,
         status: "confirmed",
-        [Op.or]: [
-          {
-            [Op.and]: [
-              { startDateTime: { [Op.not]: null } },
-              { endDateTime: { [Op.not]: null } },
-              {
-                [Op.or]: [
-                  {
-                    startDateTime: {
-                      [Op.between]: [rentalStartDateTime, rentalEndDateTime],
-                    },
-                  },
-                  {
-                    endDateTime: {
-                      [Op.between]: [rentalStartDateTime, rentalEndDateTime],
-                    },
-                  },
-                  {
-                    [Op.and]: [
-                      { startDateTime: { [Op.lte]: rentalStartDateTime } },
-                      { endDateTime: { [Op.gte]: rentalEndDateTime } },
-                    ],
-                  },
-                ],
-              },
-            ],
-          },
+        startDateTime: { [Op.not]: null },
+        endDateTime: { [Op.not]: null },
+        [Op.and]: [
+          // existingStart < newEnd (existing rental starts before new one ends)
+          { startDateTime: { [Op.lt]: rentalEndDateTime } },
+          // existingEnd > newStart (existing rental ends after new one starts)
+          { endDateTime: { [Op.gt]: rentalStartDateTime } },
         ],
       },
     });
@@ -1087,6 +1070,27 @@ router.post("/cost-preview", authenticateToken, async (req, res) => {
       });
     }
 
+    // Check for overlapping rentals (same logic as in POST /rentals)
+    // Two ranges overlap if: existingStart < newEnd AND existingEnd > newStart
+    const overlappingRental = await Rental.findOne({
+      where: {
+        itemId,
+        status: "confirmed",
+        startDateTime: { [Op.not]: null },
+        endDateTime: { [Op.not]: null },
+        [Op.and]: [
+          { startDateTime: { [Op.lt]: rentalEndDateTime } },
+          { endDateTime: { [Op.gt]: rentalStartDateTime } },
+        ],
+      },
+    });
+
+    if (overlappingRental) {
+      return res
+        .status(400)
+        .json({ error: "Item is already booked for these dates" });
+    }
+
     // Calculate rental cost using duration calculator
     const totalAmount = RentalDurationCalculator.calculateRentalCost(
       rentalStartDateTime,
diff --git a/frontend/src/pages/RentItem.tsx b/frontend/src/pages/RentItem.tsx
index 14d50f1..49517f2 100644
--- a/frontend/src/pages/RentItem.tsx
+++ b/frontend/src/pages/RentItem.tsx
@@ -420,6 +420,20 @@ const RentItem: React.FC = () => {
                           <i className="bi bi-exclamation-triangle me-2"></i>
                           {dateValidationError}
                         </div>
+                      ) : costError ? (
+                        <div className="alert alert-danger">
+                          <i className="bi bi-exclamation-triangle me-2"></i>
+                          {costError}
+                          <div className="mt-2">
+                            <button
+                              type="button"
+                              className="btn btn-outline-secondary btn-sm"
+                              onClick={() => navigate(`/items/${id}`)}
+                            >
+                              Choose Different Dates
+                            </button>
+                          </div>
+                        </div>
                       ) : !rentalDates.startDateTime ||
                         !rentalDates.endDateTime ||
                         !getRentalData() ? (