diff --git a/src/App.jsx b/src/App.jsx
index 762d28e..4b847e7 100644
--- a/src/App.jsx
+++ b/src/App.jsx
@@ -3,6 +3,7 @@ import { getNavHelper } from "internal-nav-helper";
 import { useConnect } from "redux-bundler-hook";
 import links from "./nav-links";
 import { FaGithub } from "react-icons/fa";
+import { normalizeUrlForHash } from "./app-url";
 
 const version = import.meta.env.PKG_VERSION;
 const BASE_URL = import.meta.env.BASE_URL;
@@ -38,9 +39,7 @@ function App() {
   return (
     <div
       onClick={getNavHelper((url) => {
-        // Remove BASE_URL# before it is added again by the navhelper so it can be included in the hrefs for copy url purposes
-        url = url.replace(`${BASE_URL}#`, "");
-        doUpdateHash(url);
+        doUpdateHash(normalizeUrlForHash(url, BASE_URL));
       })}
     >
       <SiteWrapper
diff --git a/src/app-url.js b/src/app-url.js
new file mode 100644
index 0000000..cc5aab1
--- /dev/null
+++ b/src/app-url.js
@@ -0,0 +1,29 @@
+// Normalizes URLs captured from click events into the hash route shape expected
+// by redux-bundler. This avoids re-appending BASE_URL or "#" and producing
+// duplicated routes when docs are hosted under a subpath.
+export function normalizeUrlForHash(url, baseUrl) {
+  if (!url) return "/";
+
+  const hashIndex = url.indexOf("#");
+  if (hashIndex >= 0) {
+    // Internal hash links are already pointing at the target route, so keep
+    // only the path after "#".
+    return url.slice(hashIndex + 1) || "/";
+  }
+
+  let basePath = "/";
+  try {
+    basePath = new URL(baseUrl, "http://localhost").pathname;
+  } catch {
+    basePath = "/";
+  }
+
+  const normalizedBasePath = `/${basePath.replace(/^\/+|\/+$/g, "")}/`;
+  if (normalizedBasePath !== "//" && url.startsWith(normalizedBasePath)) {
+    // Same-origin links without a hash still need the deploy subpath removed
+    // before they are handed to doUpdateHash.
+    return url.slice(normalizedBasePath.length - 1) || "/";
+  }
+
+  return url;
+}
diff --git a/src/app-url.test.js b/src/app-url.test.js
new file mode 100644
index 0000000..61ef49a
--- /dev/null
+++ b/src/app-url.test.js
@@ -0,0 +1,31 @@
+import { describe, expect, it } from "vitest";
+import { normalizeUrlForHash } from "./app-url";
+
+describe("normalizeUrlForHash", () => {
+  it("extracts the route from a same-origin hash URL under a base path", () => {
+    expect(
+      normalizeUrlForHash(
+        "/groundwork/#/docs/navigation/sidebar",
+        "https://usace.github.io/groundwork/",
+      ),
+    ).toBe("/docs/navigation/sidebar");
+  });
+
+  it("extracts the route from a root hash URL", () => {
+    expect(
+      normalizeUrlForHash(
+        "/#/docs/navigation/sidebar",
+        "http://localhost:5173/",
+      ),
+    ).toBe("/docs/navigation/sidebar");
+  });
+
+  it("strips the base path from non-hash same-origin URLs", () => {
+    expect(
+      normalizeUrlForHash(
+        "/groundwork/docs",
+        "https://usace.github.io/groundwork/",
+      ),
+    ).toBe("/docs");
+  });
+});