diff --git a/config/test.exs b/config/test.exs
index 21392632..ea4eae2b 100644
--- a/config/test.exs
+++ b/config/test.exs
@@ -48,6 +48,11 @@ config :microwaveprop, MicrowavepropWeb.Endpoint,
 # Run Oban jobs inline during tests
 config :microwaveprop, Oban, testing: :inline
 
+# Skip the registration-time QRZ lookup in tests — it needs a Mox stub
+# that isn't set up across the test suite, and the worker is exercised
+# directly in its own dedicated test.
+config :microwaveprop, :enable_home_qth_lookup, false
+
 # MetricsLogSuppressionTest hits GET /metrics and asserts no "Sent 200"
 # log line; that path needs PromEx alive to return a 200. We can't
 # blanket-disable PromEx. Instead, toggle off the Oban-queue poller
diff --git a/lib/microwaveprop/accounts.ex b/lib/microwaveprop/accounts.ex
index 8c66041f..dd33c6f2 100644
--- a/lib/microwaveprop/accounts.ex
+++ b/lib/microwaveprop/accounts.ex
@@ -9,8 +9,8 @@ defmodule Microwaveprop.Accounts do
   alias Microwaveprop.Accounts.UserNotifier
   alias Microwaveprop.Accounts.UserToken
   alias Microwaveprop.Repo
-
   ## Database getters
+  alias Microwaveprop.Workers.UserHomeQthLookupWorker
 
   @doc """
   Gets a user by email.
@@ -132,6 +132,47 @@ defmodule Microwaveprop.Accounts do
     %User{}
     |> User.registration_changeset(attrs)
     |> Repo.insert()
+    |> maybe_enqueue_home_qth_lookup()
+  end
+
+  defp maybe_enqueue_home_qth_lookup({:ok, %User{id: id, callsign: call} = user}) when is_binary(call) do
+    if home_qth_lookup_enabled?() do
+      worker = UserHomeQthLookupWorker
+
+      if Code.ensure_loaded?(worker) and function_exported?(worker, :new, 1) do
+        _ = %{user_id: id} |> worker.new() |> Oban.insert()
+      end
+    end
+
+    {:ok, user}
+  end
+
+  defp maybe_enqueue_home_qth_lookup(other), do: other
+
+  defp home_qth_lookup_enabled? do
+    Application.get_env(:microwaveprop, :enable_home_qth_lookup, true)
+  end
+
+  @doc """
+  Enqueue a `UserHomeQthLookupWorker` job for every user whose
+  `home_grid` is still nil. Safe to call repeatedly — the worker
+  no-ops when the user has set their QTH manually.
+  """
+  @spec backfill_missing_home_qth() :: :ok
+  def backfill_missing_home_qth do
+    worker = UserHomeQthLookupWorker
+
+    if home_qth_lookup_enabled?() and Code.ensure_loaded?(worker) and function_exported?(worker, :new, 1) do
+      User
+      |> where([u], is_nil(u.home_grid))
+      |> select([u], u.id)
+      |> Repo.all()
+      |> Enum.each(fn id ->
+        _ = %{user_id: id} |> worker.new() |> Oban.insert()
+      end)
+    end
+
+    :ok
   end
 
   @doc """
diff --git a/lib/microwaveprop/application.ex b/lib/microwaveprop/application.ex
index d7b2b1cf..f09a4a96 100644
--- a/lib/microwaveprop/application.ex
+++ b/lib/microwaveprop/application.ex
@@ -60,6 +60,13 @@ defmodule Microwaveprop.Application do
     # lifetime of the pod.
     {:ok, _pid} = Task.start(fn -> Microwaveprop.Weather.warm_grid_cache_from_latest_profile() end)
 
+    # One-shot backfill: enqueue a QRZ-lookup job for every user with a
+    # missing home QTH. Idempotent — the worker no-ops if home_grid is
+    # already set, so re-running on every boot is safe (and useful: any
+    # users registered while the worker module was unavailable get
+    # picked up the next time the pod restarts).
+    {:ok, _pid} = Task.start(fn -> Microwaveprop.Accounts.backfill_missing_home_qth() end)
+
     # Load ML model in dev/test only (Nx/Axon not compiled for prod)
     if Application.get_env(:microwaveprop, :load_ml_model, false) do
       Microwaveprop.Propagation.load_ml_model()
diff --git a/lib/microwaveprop/workers/user_home_qth_lookup_worker.ex b/lib/microwaveprop/workers/user_home_qth_lookup_worker.ex
new file mode 100644
index 00000000..e6a5772a
--- /dev/null
+++ b/lib/microwaveprop/workers/user_home_qth_lookup_worker.ex
@@ -0,0 +1,70 @@
+defmodule Microwaveprop.Workers.UserHomeQthLookupWorker do
+  @moduledoc """
+  Looks up a user's callsign via QRZ (with Google Maps fallback) and
+  populates their home QTH fields if they're still empty.
+
+  Enqueued automatically on `Accounts.register_user/1` and reusable for
+  backfilling existing users via:
+
+      Microwaveprop.Repo.all(
+        from u in Microwaveprop.Accounts.User, where: is_nil(u.home_grid)
+      )
+      |> Enum.each(fn user ->
+        %{user_id: user.id}
+        |> Microwaveprop.Workers.UserHomeQthLookupWorker.new()
+        |> Oban.insert()
+      end)
+  """
+
+  use Oban.Worker, queue: :weather, max_attempts: 3
+
+  alias Microwaveprop.Accounts
+  alias Microwaveprop.Accounts.User
+  alias Microwaveprop.Radio.CallsignClient
+  alias Microwaveprop.Radio.Maidenhead
+  alias Microwaveprop.Repo
+
+  require Logger
+
+  @impl Oban.Worker
+  def perform(%Oban.Job{args: %{"user_id" => user_id}}) do
+    case Repo.get(User, user_id) do
+      nil ->
+        :ok
+
+      %User{home_grid: grid} when is_binary(grid) and grid != "" ->
+        # User already set their home QTH manually; don't overwrite.
+        :ok
+
+      %User{callsign: nil} ->
+        :ok
+
+      %User{callsign: callsign} = user ->
+        do_lookup(user, callsign)
+    end
+  end
+
+  defp do_lookup(user, callsign) do
+    case CallsignClient.locate(callsign) do
+      {:ok, %{lat: lat, lon: lon} = result} ->
+        grid = result[:gridsquare] || Maidenhead.from_latlon(lat, lon, 10)
+        attrs = %{"home_grid" => grid, "home_lat" => lat, "home_lon" => lon}
+
+        case Accounts.update_user_home_qth(user, attrs) do
+          {:ok, _user} ->
+            :ok
+
+          {:error, changeset} ->
+            Logger.warning(
+              "UserHomeQthLookupWorker save failed: callsign=#{inspect(callsign)} errors=#{inspect(changeset.errors)}"
+            )
+
+            :ok
+        end
+
+      {:error, reason} ->
+        Logger.info("UserHomeQthLookupWorker lookup failed for #{inspect(callsign)}: #{inspect(reason)}")
+        :ok
+    end
+  end
+end
diff --git a/lib/microwaveprop_web/controllers/user_settings_html/edit.html.heex b/lib/microwaveprop_web/controllers/user_settings_html/edit.html.heex
index 9cc1e595..e7758ecb 100644
--- a/lib/microwaveprop_web/controllers/user_settings_html/edit.html.heex
+++ b/lib/microwaveprop_web/controllers/user_settings_html/edit.html.heex
@@ -32,6 +32,17 @@
         Used to anchor the rover map (drive radius, distance/bearing labels).
         Enter a Maidenhead grid (e.g. <code>EM13qc</code>) or explicit lat/lon.
       </p>
+      <div
+        :if={!@current_scope.user.home_grid}
+        class="alert alert-warning text-xs mt-2"
+      >
+        <.icon name="hero-exclamation-triangle" class="size-4 shrink-0" />
+        <span>
+          Using the default NTMS-area location (EM13).
+          A QRZ lookup for <code>{@current_scope.user.callsign}</code>
+          is queued — check back shortly, or set yours manually below.
+        </span>
+      </div>
     </div>
 
     <.input
diff --git a/test/microwaveprop/workers/user_home_qth_lookup_worker_test.exs b/test/microwaveprop/workers/user_home_qth_lookup_worker_test.exs
new file mode 100644
index 00000000..cf8aaa5c
--- /dev/null
+++ b/test/microwaveprop/workers/user_home_qth_lookup_worker_test.exs
@@ -0,0 +1,62 @@
+defmodule Microwaveprop.Workers.UserHomeQthLookupWorkerTest do
+  use Microwaveprop.DataCase, async: false
+  use Oban.Testing, repo: Microwaveprop.Repo
+
+  import Microwaveprop.AccountsFixtures
+
+  alias Microwaveprop.Repo
+  alias Microwaveprop.Workers.UserHomeQthLookupWorker
+
+  # The test config disables enqueueing on registration globally so the
+  # rest of the suite doesn't need a Mox stub. We don't toggle that here
+  # — these tests invoke the worker directly via `perform_job/2`, which
+  # is independent of the enqueue flag.
+
+  describe "perform/1" do
+    test "no-ops when the user already has a home_grid set" do
+      user =
+        user_fixture()
+        |> Ecto.Changeset.change(home_grid: "EM13qc", home_lat: 33.1, home_lon: -96.6)
+        |> Repo.update!()
+
+      assert :ok = perform_job(UserHomeQthLookupWorker, %{user_id: user.id})
+      reloaded = Repo.reload(user)
+      assert reloaded.home_grid == "EM13qc"
+    end
+
+    test "no-ops when the user no longer exists" do
+      assert :ok = perform_job(UserHomeQthLookupWorker, %{user_id: Ecto.UUID.generate()})
+    end
+
+    test "populates home QTH from a successful CallsignClient lookup" do
+      user = user_fixture()
+
+      # Stub QRZ.com HTTP layer to return coords for the user's callsign.
+      # The callsign-location pipeline reads either lat/lon or grid from
+      # the QRZ XML; we serve coords directly so the geocoder fallback
+      # isn't exercised.
+      Req.Test.stub(Microwaveprop.Qrz.Client, fn conn ->
+        Plug.Conn.send_resp(conn, 200, """
+        <?xml version="1.0" encoding="utf-8"?>
+        <QRZDatabase>
+          <Session><Key>test-session</Key></Session>
+          <Callsign>
+            <call>#{user.callsign}</call>
+            <lat>33.10</lat>
+            <lon>-96.625</lon>
+            <grid>EM13qc</grid>
+          </Callsign>
+        </QRZDatabase>
+        """)
+      end)
+
+      assert :ok = perform_job(UserHomeQthLookupWorker, %{user_id: user.id})
+
+      reloaded = Repo.reload(user)
+      assert is_binary(reloaded.home_grid)
+      assert String.starts_with?(reloaded.home_grid, "EM13qc")
+      assert is_float(reloaded.home_lat)
+      assert is_float(reloaded.home_lon)
+    end
+  end
+end