diff --git a/esphome/cpp_helpers.py b/esphome/cpp_helpers.py
index ee91ac6132..a1289485ca 100644
--- a/esphome/cpp_helpers.py
+++ b/esphome/cpp_helpers.py
@@ -17,7 +17,7 @@ from esphome.core import CORE, ID, coroutine
 from esphome.coroutine import FakeAwaitable
 from esphome.cpp_generator import MockObj, add, get_variable
 from esphome.cpp_types import App
-from esphome.helpers import sanitize, snake_case
+from esphome.entity import get_base_entity_object_id
 from esphome.types import ConfigFragmentType, ConfigType
 from esphome.util import Registry, RegistryEntry
 
@@ -122,19 +122,14 @@ async def setup_entity(var: MockObj, config: ConfigType, platform: str) -> None:
 
     add(var.set_name(config[CONF_NAME]))
 
-    # Calculate base object_id
-    base_object_id: str
+    # Calculate base object_id using the same logic as C++
+    # This must match the C++ behavior in esphome/core/entity_base.cpp
+    base_object_id = get_base_entity_object_id(config[CONF_NAME], CORE.friendly_name)
+
     if not config[CONF_NAME]:
-        # Use the friendly name if available, otherwise use the device name
-        if CORE.friendly_name:
-            base_object_id = sanitize(snake_case(CORE.friendly_name))
-        else:
-            base_object_id = sanitize(snake_case(CORE.name))
         _LOGGER.debug(
             "Entity has empty name, using '%s' as object_id base", base_object_id
         )
-    else:
-        base_object_id = sanitize(snake_case(config[CONF_NAME]))
 
     # Handle duplicates
     # Check for duplicates
@@ -156,6 +151,12 @@ async def setup_entity(var: MockObj, config: ConfigType, platform: str) -> None:
         object_id = base_object_id
 
     add(var.set_object_id(object_id))
+    _LOGGER.debug(
+        "Setting object_id '%s' for entity '%s' on platform '%s'",
+        object_id,
+        config[CONF_NAME],
+        platform,
+    )
     add(var.set_disabled_by_default(config[CONF_DISABLED_BY_DEFAULT]))
     if CONF_INTERNAL in config:
         add(var.set_internal(config[CONF_INTERNAL]))
diff --git a/esphome/entity.py b/esphome/entity.py
new file mode 100644
index 0000000000..732822d0ff
--- /dev/null
+++ b/esphome/entity.py
@@ -0,0 +1,41 @@
+"""Entity-related helper functions."""
+
+from esphome.core import CORE
+from esphome.helpers import sanitize, snake_case
+
+
+def get_base_entity_object_id(name: str, friendly_name: str | None) -> str:
+    """Calculate the base object ID for an entity that will be set via set_object_id().
+
+    This function calculates what object_id_c_str_ should be set to in C++.
+
+    The C++ EntityBase::get_object_id() (entity_base.cpp lines 38-49) works as:
+    - If !has_own_name && is_name_add_mac_suffix_enabled():
+        return str_sanitize(str_snake_case(App.get_friendly_name()))  // Dynamic
+    - Else:
+        return object_id_c_str_ ?? ""  // What we set via set_object_id()
+
+    Since we're calculating what to pass to set_object_id(), we always need to
+    generate the object_id the same way, regardless of name_add_mac_suffix setting.
+
+    Args:
+        name: The entity name (empty string if no name)
+        friendly_name: The friendly name from CORE.friendly_name
+
+    Returns:
+        The base object ID to use for duplicate checking and to pass to set_object_id()
+    """
+
+    if name:
+        # Entity has its own name (has_own_name will be true)
+        base_str = name
+    elif friendly_name:
+        # Entity has empty name (has_own_name will be false)
+        # Calculate what the object_id should be
+        # C++ uses App.get_friendly_name() which returns friendly_name or device name
+        base_str = friendly_name
+    else:
+        # Fallback to device name
+        base_str = CORE.name
+
+    return sanitize(snake_case(base_str))
diff --git a/tests/integration/fixtures/duplicate_entities.yaml b/tests/integration/fixtures/duplicate_entities.yaml
new file mode 100644
index 0000000000..0f831db90d
--- /dev/null
+++ b/tests/integration/fixtures/duplicate_entities.yaml
@@ -0,0 +1,118 @@
+esphome:
+  name: duplicate-entities-test
+  # Define devices to test multi-device duplicate handling
+  devices:
+    - id: controller_1
+      name: Controller 1
+    - id: controller_2
+      name: Controller 2
+
+host:
+api:  # Port will be automatically injected
+logger:
+
+# Create duplicate entities across different scenarios
+
+# Scenario 1: Multiple sensors with same name on same device (should get _2, _3, _4)
+sensor:
+  - platform: template
+    name: Temperature
+    lambda: return 1.0;
+    update_interval: 0.1s
+
+  - platform: template
+    name: Temperature
+    lambda: return 2.0;
+    update_interval: 0.1s
+
+  - platform: template
+    name: Temperature
+    lambda: return 3.0;
+    update_interval: 0.1s
+
+  - platform: template
+    name: Temperature
+    lambda: return 4.0;
+    update_interval: 0.1s
+
+  # Scenario 2: Device-specific duplicates using device_id configuration
+  - platform: template
+    name: Device Temperature
+    device_id: controller_1
+    lambda: return 10.0;
+    update_interval: 0.1s
+
+  - platform: template
+    name: Device Temperature
+    device_id: controller_1
+    lambda: return 11.0;
+    update_interval: 0.1s
+
+  - platform: template
+    name: Device Temperature
+    device_id: controller_1
+    lambda: return 12.0;
+    update_interval: 0.1s
+
+  # Different device, same name - should not conflict
+  - platform: template
+    name: Device Temperature
+    device_id: controller_2
+    lambda: return 20.0;
+    update_interval: 0.1s
+
+# Scenario 3: Binary sensors (different platform, same name)
+binary_sensor:
+  - platform: template
+    name: Temperature
+    lambda: return true;
+
+  - platform: template
+    name: Temperature
+    lambda: return false;
+
+  - platform: template
+    name: Temperature
+    lambda: return true;
+
+  # Scenario 5: Binary sensors on devices
+  - platform: template
+    name: Device Temperature
+    device_id: controller_1
+    lambda: return true;
+
+  - platform: template
+    name: Device Temperature
+    device_id: controller_2
+    lambda: return false;
+
+# Scenario 6: Test with special characters that need sanitization
+text_sensor:
+  - platform: template
+    name: "Status Message!"
+    lambda: return {"status1"};
+    update_interval: 0.1s
+
+  - platform: template
+    name: "Status Message!"
+    lambda: return {"status2"};
+    update_interval: 0.1s
+
+  - platform: template
+    name: "Status Message!"
+    lambda: return {"status3"};
+    update_interval: 0.1s
+
+# Scenario 7: More switch duplicates
+switch:
+  - platform: template
+    name: "Power Switch"
+    lambda: return false;
+    turn_on_action: []
+    turn_off_action: []
+
+  - platform: template
+    name: "Power Switch"
+    lambda: return true;
+    turn_on_action: []
+    turn_off_action: []
diff --git a/tests/integration/test_duplicate_entities.py b/tests/integration/test_duplicate_entities.py
new file mode 100644
index 0000000000..edbcb9799c
--- /dev/null
+++ b/tests/integration/test_duplicate_entities.py
@@ -0,0 +1,187 @@
+"""Integration test for duplicate entity handling."""
+
+from __future__ import annotations
+
+import asyncio
+
+from aioesphomeapi import EntityInfo
+import pytest
+
+from .types import APIClientConnectedFactory, RunCompiledFunction
+
+
+@pytest.mark.asyncio
+async def test_duplicate_entities(
+    yaml_config: str,
+    run_compiled: RunCompiledFunction,
+    api_client_connected: APIClientConnectedFactory,
+) -> None:
+    """Test that duplicate entity names are automatically suffixed with _2, _3, _4."""
+    async with run_compiled(yaml_config), api_client_connected() as client:
+        # Get device info
+        device_info = await client.device_info()
+        assert device_info is not None
+
+        # Get devices
+        devices = device_info.devices
+        assert len(devices) >= 2, f"Expected at least 2 devices, got {len(devices)}"
+
+        # Find our test devices
+        controller_1 = next((d for d in devices if d.name == "Controller 1"), None)
+        controller_2 = next((d for d in devices if d.name == "Controller 2"), None)
+
+        assert controller_1 is not None, "Controller 1 device not found"
+        assert controller_2 is not None, "Controller 2 device not found"
+
+        # Get entity list
+        entities = await client.list_entities_services()
+        all_entities: list[EntityInfo] = []
+        for entity_list in entities[0]:
+            if hasattr(entity_list, "object_id"):
+                all_entities.append(entity_list)
+
+        # Group entities by type for easier testing
+        sensors = [e for e in all_entities if e.__class__.__name__ == "SensorInfo"]
+        binary_sensors = [
+            e for e in all_entities if e.__class__.__name__ == "BinarySensorInfo"
+        ]
+        text_sensors = [
+            e for e in all_entities if e.__class__.__name__ == "TextSensorInfo"
+        ]
+        switches = [e for e in all_entities if e.__class__.__name__ == "SwitchInfo"]
+
+        # Scenario 1: Check sensors with duplicate "Temperature" names
+        temp_sensors = [s for s in sensors if s.name == "Temperature"]
+        temp_object_ids = sorted([s.object_id for s in temp_sensors])
+
+        # Should have temperature, temperature_2, temperature_3, temperature_4
+        assert len(temp_object_ids) >= 4, (
+            f"Expected at least 4 temperature sensors, got {len(temp_object_ids)}"
+        )
+        assert "temperature" in temp_object_ids, (
+            "First temperature sensor should not have suffix"
+        )
+        assert "temperature_2" in temp_object_ids, (
+            "Second temperature sensor should be temperature_2"
+        )
+        assert "temperature_3" in temp_object_ids, (
+            "Third temperature sensor should be temperature_3"
+        )
+        assert "temperature_4" in temp_object_ids, (
+            "Fourth temperature sensor should be temperature_4"
+        )
+
+        # Scenario 2: Check device-specific sensors don't conflict
+        device_temp_sensors = [s for s in sensors if s.name == "Device Temperature"]
+
+        # Group by device
+        controller_1_temps = [
+            s
+            for s in device_temp_sensors
+            if getattr(s, "device_id", None) == controller_1.device_id
+        ]
+        controller_2_temps = [
+            s
+            for s in device_temp_sensors
+            if getattr(s, "device_id", None) == controller_2.device_id
+        ]
+
+        # Controller 1 should have device_temperature, device_temperature_2, device_temperature_3
+        c1_object_ids = sorted([s.object_id for s in controller_1_temps])
+        assert len(c1_object_ids) >= 3, (
+            f"Expected at least 3 sensors on controller_1, got {len(c1_object_ids)}"
+        )
+        assert "device_temperature" in c1_object_ids, (
+            "First device sensor should not have suffix"
+        )
+        assert "device_temperature_2" in c1_object_ids, (
+            "Second device sensor should be device_temperature_2"
+        )
+        assert "device_temperature_3" in c1_object_ids, (
+            "Third device sensor should be device_temperature_3"
+        )
+
+        # Controller 2 should have only device_temperature (no suffix)
+        c2_object_ids = [s.object_id for s in controller_2_temps]
+        assert len(c2_object_ids) >= 1, (
+            f"Expected at least 1 sensor on controller_2, got {len(c2_object_ids)}"
+        )
+        assert "device_temperature" in c2_object_ids, (
+            "Controller 2 sensor should not have suffix"
+        )
+
+        # Scenario 3: Check binary sensors (different platform, same name)
+        temp_binary = [b for b in binary_sensors if b.name == "Temperature"]
+        binary_object_ids = sorted([b.object_id for b in temp_binary])
+
+        # Should have temperature, temperature_2, temperature_3 (no conflict with sensor platform)
+        assert len(binary_object_ids) >= 3, (
+            f"Expected at least 3 binary sensors, got {len(binary_object_ids)}"
+        )
+        assert "temperature" in binary_object_ids, (
+            "First binary sensor should not have suffix"
+        )
+        assert "temperature_2" in binary_object_ids, (
+            "Second binary sensor should be temperature_2"
+        )
+        assert "temperature_3" in binary_object_ids, (
+            "Third binary sensor should be temperature_3"
+        )
+
+        # Scenario 4: Check text sensors with special characters
+        status_sensors = [t for t in text_sensors if t.name == "Status Message!"]
+        status_object_ids = sorted([t.object_id for t in status_sensors])
+
+        # Special characters should be sanitized to _
+        assert len(status_object_ids) >= 3, (
+            f"Expected at least 3 status sensors, got {len(status_object_ids)}"
+        )
+        assert "status_message_" in status_object_ids, (
+            "First status sensor should be status_message_"
+        )
+        assert "status_message__2" in status_object_ids, (
+            "Second status sensor should be status_message__2"
+        )
+        assert "status_message__3" in status_object_ids, (
+            "Third status sensor should be status_message__3"
+        )
+
+        # Scenario 5: Check switches with duplicate names
+        power_switches = [s for s in switches if s.name == "Power Switch"]
+        power_object_ids = sorted([s.object_id for s in power_switches])
+
+        # Should have power_switch, power_switch_2
+        assert len(power_object_ids) >= 2, (
+            f"Expected at least 2 power switches, got {len(power_object_ids)}"
+        )
+        assert "power_switch" in power_object_ids, (
+            "First power switch should be power_switch"
+        )
+        assert "power_switch_2" in power_object_ids, (
+            "Second power switch should be power_switch_2"
+        )
+
+        # Verify we can get states for all entities (ensures they're functional)
+        loop = asyncio.get_running_loop()
+        states_future: asyncio.Future[bool] = loop.create_future()
+        state_count = 0
+        expected_count = (
+            len(sensors) + len(binary_sensors) + len(text_sensors) + len(switches)
+        )
+
+        def on_state(state) -> None:
+            nonlocal state_count
+            state_count += 1
+            if state_count >= expected_count and not states_future.done():
+                states_future.set_result(True)
+
+        client.subscribe_states(on_state)
+
+        # Wait for all entity states
+        try:
+            await asyncio.wait_for(states_future, timeout=10.0)
+        except asyncio.TimeoutError:
+            pytest.fail(
+                f"Did not receive all entity states within 10 seconds. "
+                f"Expected {expected_count}, received {state_count}"
+            )
diff --git a/tests/unit_tests/test_get_base_entity_object_id.py b/tests/unit_tests/test_get_base_entity_object_id.py
new file mode 100644
index 0000000000..aeea862d78
--- /dev/null
+++ b/tests/unit_tests/test_get_base_entity_object_id.py
@@ -0,0 +1,140 @@
+"""Test get_base_entity_object_id function matches C++ behavior."""
+
+from esphome.core import CORE
+from esphome.entity import get_base_entity_object_id
+from esphome.helpers import sanitize, snake_case
+
+
+class TestGetBaseEntityObjectId:
+    """Test that get_base_entity_object_id matches C++ EntityBase::get_object_id behavior."""
+
+    def test_with_entity_name(self) -> None:
+        """Test when entity has its own name - should use entity name."""
+        # Simple name
+        assert (
+            get_base_entity_object_id("Temperature Sensor", None)
+            == "temperature_sensor"
+        )
+        assert (
+            get_base_entity_object_id("Temperature Sensor", "Device Name")
+            == "temperature_sensor"
+        )
+
+        # Name with special characters
+        assert (
+            get_base_entity_object_id("Temp!@#$%^&*()Sensor", None)
+            == "temp__________sensor"
+        )
+        assert get_base_entity_object_id("Temp-Sensor_123", None) == "temp-sensor_123"
+
+        # Already snake_case
+        assert (
+            get_base_entity_object_id("temperature_sensor", None)
+            == "temperature_sensor"
+        )
+
+        # Mixed case
+        assert (
+            get_base_entity_object_id("TemperatureSensor", None) == "temperaturesensor"
+        )
+        assert (
+            get_base_entity_object_id("TEMPERATURE SENSOR", None)
+            == "temperature_sensor"
+        )
+
+    def test_empty_name_with_friendly_name(self) -> None:
+        """Test when entity has empty name - should use friendly name."""
+        # C++ behavior: when has_own_name is false, uses App.get_friendly_name()
+        assert get_base_entity_object_id("", "Friendly Device") == "friendly_device"
+        assert (
+            get_base_entity_object_id("", "Kitchen Controller") == "kitchen_controller"
+        )
+        assert get_base_entity_object_id("", "Test-Device_123") == "test-device_123"
+
+        # Special characters in friendly name
+        assert get_base_entity_object_id("", "Device!@#$%") == "device_____"
+
+    def test_empty_name_no_friendly_name(self) -> None:
+        """Test when entity has empty name and no friendly name - should use device name."""
+        # Save original values
+        original_name = getattr(CORE, "name", None)
+
+        try:
+            # Test with CORE.name set
+            CORE.name = "device-name"
+            assert get_base_entity_object_id("", None) == "device-name"
+
+            CORE.name = "Test Device"
+            assert get_base_entity_object_id("", None) == "test_device"
+
+        finally:
+            # Restore original value
+            if original_name is not None:
+                CORE.name = original_name
+
+    def test_edge_cases(self) -> None:
+        """Test edge cases."""
+        # Only spaces
+        assert get_base_entity_object_id("   ", None) == "___"
+
+        # Unicode characters (should be replaced)
+        assert get_base_entity_object_id("Température", None) == "temp_rature"
+        assert get_base_entity_object_id("测试", None) == "__"
+
+        # Empty string with empty friendly name (empty friendly name is treated as None)
+        # Falls back to CORE.name
+        original_name = getattr(CORE, "name", None)
+        try:
+            CORE.name = "device"
+            assert get_base_entity_object_id("", "") == "device"
+        finally:
+            if original_name is not None:
+                CORE.name = original_name
+
+        # Very long name (should work fine)
+        long_name = "a" * 100 + " " + "b" * 100
+        expected = "a" * 100 + "_" + "b" * 100
+        assert get_base_entity_object_id(long_name, None) == expected
+
+    def test_matches_cpp_helpers(self) -> None:
+        """Test that the logic matches using snake_case and sanitize directly."""
+        test_cases = [
+            ("Temperature Sensor", "temperature_sensor"),
+            ("Living Room Light", "living_room_light"),
+            ("Test-Device_123", "test-device_123"),
+            ("Special!@#Chars", "special___chars"),
+            ("UPPERCASE NAME", "uppercase_name"),
+            ("lowercase name", "lowercase_name"),
+            ("Mixed Case Name", "mixed_case_name"),
+            ("   Spaces   ", "___spaces___"),
+        ]
+
+        for name, expected in test_cases:
+            # For non-empty names, verify our function produces same result as direct snake_case + sanitize
+            assert get_base_entity_object_id(name, None) == sanitize(snake_case(name))
+            assert get_base_entity_object_id(name, None) == expected
+
+        # Empty name is handled specially - it doesn't just use sanitize(snake_case(""))
+        # Instead it falls back to friendly_name or CORE.name
+        assert sanitize(snake_case("")) == ""  # Direct conversion gives empty string
+        # But our function returns a fallback
+        original_name = getattr(CORE, "name", None)
+        try:
+            CORE.name = "device"
+            assert get_base_entity_object_id("", None) == "device"  # Uses device name
+        finally:
+            if original_name is not None:
+                CORE.name = original_name
+
+    def test_name_add_mac_suffix_behavior(self) -> None:
+        """Test behavior related to name_add_mac_suffix.
+
+        In C++, when name_add_mac_suffix is enabled and entity has no name,
+        get_object_id() returns str_sanitize(str_snake_case(App.get_friendly_name()))
+        dynamically. Our function always returns the same result since we're
+        calculating the base for duplicate tracking.
+        """
+        # The function should always return the same result regardless of
+        # name_add_mac_suffix setting, as we're calculating the base object_id
+        assert get_base_entity_object_id("", "Test Device") == "test_device"
+        assert get_base_entity_object_id("Entity Name", "Test Device") == "entity_name"