diff --git a/lib/towerops/gaiia/site_aggregation.ex b/lib/towerops/gaiia/site_aggregation.ex
new file mode 100644
index 00000000..c374e361
--- /dev/null
+++ b/lib/towerops/gaiia/site_aggregation.ex
@@ -0,0 +1,104 @@
+defmodule Towerops.Gaiia.SiteAggregation do
+  @moduledoc """
+  Computes per-site subscriber counts and MRR by matching inventory item
+  IP addresses against network site CIDR blocks.
+  """
+
+  import Ecto.Query
+
+  alias Towerops.Gaiia.Account
+  alias Towerops.Gaiia.BillingSubscription
+  alias Towerops.Gaiia.InventoryItem
+  alias Towerops.Gaiia.NetworkSite
+  alias Towerops.Repo
+
+  require Logger
+
+  @doc """
+  For each network site with IP blocks, finds inventory items whose IP addresses
+  fall within those blocks, then counts unique accounts with active subscriptions
+  and sums their MRR.
+
+  Updates each network site's `account_count` and `total_mrr` fields.
+  """
+  def compute_and_store(organization_id) do
+    sites = load_sites_with_ip_blocks(organization_id)
+    items = load_assigned_items(organization_id)
+
+    Enum.each(sites, fn site ->
+      cidrs = parse_cidrs(site.ip_blocks)
+      matched_account_ids = match_accounts_to_cidrs(items, cidrs)
+      {account_count, total_mrr} = compute_totals(organization_id, matched_account_ids)
+      update_site_totals(site, account_count, total_mrr)
+    end)
+  end
+
+  defp load_sites_with_ip_blocks(organization_id) do
+    NetworkSite
+    |> where(organization_id: ^organization_id)
+    |> where([ns], fragment("cardinality(?) > 0", ns.ip_blocks))
+    |> Repo.all()
+  end
+
+  defp load_assigned_items(organization_id) do
+    InventoryItem
+    |> where(organization_id: ^organization_id)
+    |> where([ii], not is_nil(ii.assigned_account_gaiia_id))
+    |> where([ii], not is_nil(ii.ip_address))
+    |> Repo.all()
+  end
+
+  defp parse_cidrs(ip_blocks) do
+    Enum.flat_map(ip_blocks, fn block ->
+      case InetCidr.parse_cidr(block) do
+        {:ok, cidr} -> [cidr]
+        _ -> []
+      end
+    end)
+  end
+
+  defp match_accounts_to_cidrs(items, cidrs) do
+    items
+    |> Enum.filter(fn item -> ip_in_any_cidr?(item.ip_address, cidrs) end)
+    |> Enum.map(& &1.assigned_account_gaiia_id)
+    |> Enum.uniq()
+  end
+
+  defp ip_in_any_cidr?(ip_string, cidrs) do
+    case :inet.parse_address(String.to_charlist(ip_string)) do
+      {:ok, addr} ->
+        Enum.any?(cidrs, fn cidr -> InetCidr.contains?(cidr, addr) end)
+
+      _ ->
+        false
+    end
+  end
+
+  defp compute_totals(_organization_id, []) do
+    {0, Decimal.new("0")}
+  end
+
+  defp compute_totals(organization_id, account_gaiia_ids) do
+    account_count =
+      Account
+      |> where(organization_id: ^organization_id)
+      |> where([a], a.gaiia_id in ^account_gaiia_ids)
+      |> where([a], a.subscription_count > 0)
+      |> Repo.aggregate(:count)
+
+    total_mrr =
+      BillingSubscription
+      |> where(organization_id: ^organization_id)
+      |> where([bs], bs.account_gaiia_id in ^account_gaiia_ids)
+      |> where(status: "ACTIVE")
+      |> Repo.aggregate(:sum, :mrr_amount) || Decimal.new("0")
+
+    {account_count, total_mrr}
+  end
+
+  defp update_site_totals(site, account_count, total_mrr) do
+    site
+    |> Ecto.Changeset.change(%{account_count: account_count, total_mrr: total_mrr})
+    |> Repo.update()
+  end
+end
diff --git a/lib/towerops/gaiia/sync.ex b/lib/towerops/gaiia/sync.ex
index dd2e2fe5..cb3c6435 100644
--- a/lib/towerops/gaiia/sync.ex
+++ b/lib/towerops/gaiia/sync.ex
@@ -38,6 +38,7 @@ defmodule Towerops.Gaiia.Sync do
 
       Integrations.update_sync_status(integration, "success", message)
       persist_billing_totals(integration)
+      Gaiia.SiteAggregation.compute_and_store(org_id)
 
       {:ok,
        %{
diff --git a/test/towerops/gaiia/site_aggregation_test.exs b/test/towerops/gaiia/site_aggregation_test.exs
new file mode 100644
index 00000000..ab8113c6
--- /dev/null
+++ b/test/towerops/gaiia/site_aggregation_test.exs
@@ -0,0 +1,391 @@
+defmodule Towerops.Gaiia.SiteAggregationTest do
+  use Towerops.DataCase, async: true
+
+  import Towerops.AccountsFixtures
+  import Towerops.OrganizationsFixtures
+
+  alias Towerops.Gaiia
+  alias Towerops.Gaiia.SiteAggregation
+
+  setup do
+    user = user_fixture()
+    org = organization_fixture(user.id)
+    %{org: org}
+  end
+
+  describe "compute_and_store/1" do
+    test "matches account to site via IP block", %{org: org} do
+      {:ok, _site} =
+        Gaiia.upsert_network_site(org.id, %{
+          gaiia_id: "ns-1",
+          name: "Tower A",
+          ip_blocks: ["10.0.0.0/24"]
+        })
+
+      {:ok, _account} =
+        Gaiia.upsert_account(org.id, %{
+          gaiia_id: "acct-1",
+          name: "Alice",
+          subscription_count: 1
+        })
+
+      {:ok, _item} =
+        Gaiia.upsert_inventory_item(org.id, %{
+          gaiia_id: "item-1",
+          name: "CPE",
+          ip_address: "10.0.0.5",
+          assigned_account_gaiia_id: "acct-1"
+        })
+
+      {:ok, _sub} =
+        Gaiia.upsert_billing_subscription(org.id, %{
+          gaiia_id: "sub-1",
+          account_gaiia_id: "acct-1",
+          status: "ACTIVE",
+          mrr_amount: Decimal.new("79.99")
+        })
+
+      SiteAggregation.compute_and_store(org.id)
+
+      site = Gaiia.get_network_site(org.id, "ns-1")
+      assert site.account_count == 1
+      assert Decimal.equal?(site.total_mrr, Decimal.new("79.99"))
+    end
+
+    test "counts multiple accounts at one site", %{org: org} do
+      {:ok, _} =
+        Gaiia.upsert_network_site(org.id, %{
+          gaiia_id: "ns-1",
+          name: "Tower A",
+          ip_blocks: ["10.0.0.0/24"]
+        })
+
+      {:ok, _} =
+        Gaiia.upsert_account(org.id, %{
+          gaiia_id: "acct-1",
+          name: "Alice",
+          subscription_count: 1
+        })
+
+      {:ok, _} =
+        Gaiia.upsert_account(org.id, %{
+          gaiia_id: "acct-2",
+          name: "Bob",
+          subscription_count: 1
+        })
+
+      {:ok, _} =
+        Gaiia.upsert_inventory_item(org.id, %{
+          gaiia_id: "item-1",
+          name: "CPE-1",
+          ip_address: "10.0.0.5",
+          assigned_account_gaiia_id: "acct-1"
+        })
+
+      {:ok, _} =
+        Gaiia.upsert_inventory_item(org.id, %{
+          gaiia_id: "item-2",
+          name: "CPE-2",
+          ip_address: "10.0.0.6",
+          assigned_account_gaiia_id: "acct-2"
+        })
+
+      {:ok, _} =
+        Gaiia.upsert_billing_subscription(org.id, %{
+          gaiia_id: "sub-1",
+          account_gaiia_id: "acct-1",
+          status: "ACTIVE",
+          mrr_amount: Decimal.new("50.00")
+        })
+
+      {:ok, _} =
+        Gaiia.upsert_billing_subscription(org.id, %{
+          gaiia_id: "sub-2",
+          account_gaiia_id: "acct-2",
+          status: "ACTIVE",
+          mrr_amount: Decimal.new("75.00")
+        })
+
+      SiteAggregation.compute_and_store(org.id)
+
+      site = Gaiia.get_network_site(org.id, "ns-1")
+      assert site.account_count == 2
+      assert Decimal.equal?(site.total_mrr, Decimal.new("125.00"))
+    end
+
+    test "excludes accounts with no active subscriptions", %{org: org} do
+      {:ok, _} =
+        Gaiia.upsert_network_site(org.id, %{
+          gaiia_id: "ns-1",
+          name: "Tower A",
+          ip_blocks: ["10.0.0.0/24"]
+        })
+
+      {:ok, _} =
+        Gaiia.upsert_account(org.id, %{
+          gaiia_id: "acct-no-subs",
+          name: "Charlie",
+          subscription_count: 0
+        })
+
+      {:ok, _} =
+        Gaiia.upsert_inventory_item(org.id, %{
+          gaiia_id: "item-1",
+          name: "CPE",
+          ip_address: "10.0.0.10",
+          assigned_account_gaiia_id: "acct-no-subs"
+        })
+
+      SiteAggregation.compute_and_store(org.id)
+
+      site = Gaiia.get_network_site(org.id, "ns-1")
+      assert site.account_count == 0
+      assert Decimal.equal?(site.total_mrr, Decimal.new("0"))
+    end
+
+    test "ignores items assigned to sites (not accounts)", %{org: org} do
+      {:ok, _} =
+        Gaiia.upsert_network_site(org.id, %{
+          gaiia_id: "ns-1",
+          name: "Tower A",
+          ip_blocks: ["10.0.0.0/24"]
+        })
+
+      {:ok, _} =
+        Gaiia.upsert_inventory_item(org.id, %{
+          gaiia_id: "item-infra",
+          name: "AP",
+          ip_address: "10.0.0.1",
+          assigned_network_site_gaiia_id: "ns-1",
+          assigned_account_gaiia_id: nil
+        })
+
+      SiteAggregation.compute_and_store(org.id)
+
+      site = Gaiia.get_network_site(org.id, "ns-1")
+      assert site.account_count == 0
+      assert Decimal.equal?(site.total_mrr, Decimal.new("0"))
+    end
+
+    test "matches across multiple IP blocks on one site", %{org: org} do
+      {:ok, _} =
+        Gaiia.upsert_network_site(org.id, %{
+          gaiia_id: "ns-1",
+          name: "Tower A",
+          ip_blocks: ["10.0.0.0/24", "172.16.0.0/16"]
+        })
+
+      {:ok, _} =
+        Gaiia.upsert_account(org.id, %{
+          gaiia_id: "acct-1",
+          name: "Alice",
+          subscription_count: 1
+        })
+
+      {:ok, _} =
+        Gaiia.upsert_account(org.id, %{
+          gaiia_id: "acct-2",
+          name: "Bob",
+          subscription_count: 1
+        })
+
+      {:ok, _} =
+        Gaiia.upsert_inventory_item(org.id, %{
+          gaiia_id: "item-1",
+          name: "CPE-1",
+          ip_address: "10.0.0.50",
+          assigned_account_gaiia_id: "acct-1"
+        })
+
+      {:ok, _} =
+        Gaiia.upsert_inventory_item(org.id, %{
+          gaiia_id: "item-2",
+          name: "CPE-2",
+          ip_address: "172.16.5.10",
+          assigned_account_gaiia_id: "acct-2"
+        })
+
+      {:ok, _} =
+        Gaiia.upsert_billing_subscription(org.id, %{
+          gaiia_id: "sub-1",
+          account_gaiia_id: "acct-1",
+          status: "ACTIVE",
+          mrr_amount: Decimal.new("50.00")
+        })
+
+      {:ok, _} =
+        Gaiia.upsert_billing_subscription(org.id, %{
+          gaiia_id: "sub-2",
+          account_gaiia_id: "acct-2",
+          status: "ACTIVE",
+          mrr_amount: Decimal.new("75.00")
+        })
+
+      SiteAggregation.compute_and_store(org.id)
+
+      site = Gaiia.get_network_site(org.id, "ns-1")
+      assert site.account_count == 2
+      assert Decimal.equal?(site.total_mrr, Decimal.new("125.00"))
+    end
+
+    test "skips sites with empty ip_blocks", %{org: org} do
+      {:ok, _} =
+        Gaiia.upsert_network_site(org.id, %{
+          gaiia_id: "ns-empty",
+          name: "No Blocks",
+          ip_blocks: []
+        })
+
+      SiteAggregation.compute_and_store(org.id)
+
+      site = Gaiia.get_network_site(org.id, "ns-empty")
+      # Site was skipped — values remain at DB defaults (not computed)
+      assert site.account_count == 0
+      assert is_nil(site.total_mrr)
+    end
+
+    test "cross-site isolation — IP matches only the correct site", %{org: org} do
+      {:ok, _} =
+        Gaiia.upsert_network_site(org.id, %{
+          gaiia_id: "ns-a",
+          name: "Tower A",
+          ip_blocks: ["10.0.0.0/24"]
+        })
+
+      {:ok, _} =
+        Gaiia.upsert_network_site(org.id, %{
+          gaiia_id: "ns-b",
+          name: "Tower B",
+          ip_blocks: ["192.168.0.0/24"]
+        })
+
+      {:ok, _} =
+        Gaiia.upsert_account(org.id, %{
+          gaiia_id: "acct-1",
+          name: "Alice",
+          subscription_count: 1
+        })
+
+      {:ok, _} =
+        Gaiia.upsert_inventory_item(org.id, %{
+          gaiia_id: "item-1",
+          name: "CPE",
+          ip_address: "10.0.0.5",
+          assigned_account_gaiia_id: "acct-1"
+        })
+
+      {:ok, _} =
+        Gaiia.upsert_billing_subscription(org.id, %{
+          gaiia_id: "sub-1",
+          account_gaiia_id: "acct-1",
+          status: "ACTIVE",
+          mrr_amount: Decimal.new("60.00")
+        })
+
+      SiteAggregation.compute_and_store(org.id)
+
+      site_a = Gaiia.get_network_site(org.id, "ns-a")
+      assert site_a.account_count == 1
+      assert Decimal.equal?(site_a.total_mrr, Decimal.new("60.00"))
+
+      site_b = Gaiia.get_network_site(org.id, "ns-b")
+      assert site_b.account_count == 0
+      assert Decimal.equal?(site_b.total_mrr, Decimal.new("0"))
+    end
+
+    test "deduplicates accounts with multiple inventory items", %{org: org} do
+      {:ok, _} =
+        Gaiia.upsert_network_site(org.id, %{
+          gaiia_id: "ns-1",
+          name: "Tower A",
+          ip_blocks: ["10.0.0.0/24"]
+        })
+
+      {:ok, _} =
+        Gaiia.upsert_account(org.id, %{
+          gaiia_id: "acct-1",
+          name: "Alice",
+          subscription_count: 1
+        })
+
+      # Two items for the same account
+      {:ok, _} =
+        Gaiia.upsert_inventory_item(org.id, %{
+          gaiia_id: "item-1",
+          name: "CPE-Primary",
+          ip_address: "10.0.0.5",
+          assigned_account_gaiia_id: "acct-1"
+        })
+
+      {:ok, _} =
+        Gaiia.upsert_inventory_item(org.id, %{
+          gaiia_id: "item-2",
+          name: "CPE-Secondary",
+          ip_address: "10.0.0.6",
+          assigned_account_gaiia_id: "acct-1"
+        })
+
+      {:ok, _} =
+        Gaiia.upsert_billing_subscription(org.id, %{
+          gaiia_id: "sub-1",
+          account_gaiia_id: "acct-1",
+          status: "ACTIVE",
+          mrr_amount: Decimal.new("99.99")
+        })
+
+      SiteAggregation.compute_and_store(org.id)
+
+      site = Gaiia.get_network_site(org.id, "ns-1")
+      # Account counted once despite two items
+      assert site.account_count == 1
+      assert Decimal.equal?(site.total_mrr, Decimal.new("99.99"))
+    end
+
+    test "only sums MRR from ACTIVE subscriptions", %{org: org} do
+      {:ok, _} =
+        Gaiia.upsert_network_site(org.id, %{
+          gaiia_id: "ns-1",
+          name: "Tower A",
+          ip_blocks: ["10.0.0.0/24"]
+        })
+
+      {:ok, _} =
+        Gaiia.upsert_account(org.id, %{
+          gaiia_id: "acct-1",
+          name: "Alice",
+          subscription_count: 1
+        })
+
+      {:ok, _} =
+        Gaiia.upsert_inventory_item(org.id, %{
+          gaiia_id: "item-1",
+          name: "CPE",
+          ip_address: "10.0.0.5",
+          assigned_account_gaiia_id: "acct-1"
+        })
+
+      {:ok, _} =
+        Gaiia.upsert_billing_subscription(org.id, %{
+          gaiia_id: "sub-active",
+          account_gaiia_id: "acct-1",
+          status: "ACTIVE",
+          mrr_amount: Decimal.new("50.00")
+        })
+
+      {:ok, _} =
+        Gaiia.upsert_billing_subscription(org.id, %{
+          gaiia_id: "sub-cancelled",
+          account_gaiia_id: "acct-1",
+          status: "CANCELLED",
+          mrr_amount: Decimal.new("25.00")
+        })
+
+      SiteAggregation.compute_and_store(org.id)
+
+      site = Gaiia.get_network_site(org.id, "ns-1")
+      assert site.account_count == 1
+      # Only the active subscription's MRR
+      assert Decimal.equal?(site.total_mrr, Decimal.new("50.00"))
+    end
+  end
+end