diff --git a/lib/build-pages/compute-page-url.js b/lib/build-pages/compute-page-url.js
new file mode 100644
index 0000000..94f3f01
--- /dev/null
+++ b/lib/build-pages/compute-page-url.js
@@ -0,0 +1,17 @@
+import { fsPathToUrlPath } from './page-builders/fs-path-to-url.js'
+
+/**
+ * Derive the canonical URL path for a page from its filesystem path and output name.
+ * Index pages get a trailing-slash URL; other outputs include the filename.
+ *
+ * @param {object} params
+ * @param {string} params.path - The page's directory path relative to src root
+ * @param {string} params.outputName - The output filename (e.g. 'index.html' or 'loose-md.html')
+ * @returns {string}
+ */
+export function computePageUrl ({ path, outputName }) {
+  if (outputName === 'index.html') {
+    return path ? fsPathToUrlPath(path) + '/' : '/'
+  }
+  return path ? fsPathToUrlPath(path) + '/' + outputName : '/' + outputName
+}
diff --git a/lib/build-pages/page-data.js b/lib/build-pages/page-data.js
index 0cafe0f..af078b9 100644
--- a/lib/build-pages/page-data.js
+++ b/lib/build-pages/page-data.js
@@ -6,6 +6,7 @@
 
 import { resolveVars, resolvePostVars } from './resolve-vars.js'
 import { pageBuilders } from './page-builders/index.js'
+import { computePageUrl } from './compute-page-url.js'
 // @ts-expect-error
 import pretty from 'pretty'
 
@@ -141,6 +142,7 @@ export class PageData {
     const { globalVars, globalDataVars, pageVars, builderVars } = this
     // @ts-ignore
     return {
+      pageUrl: this.#computePageUrl(),
       ...globalVars,
       ...globalDataVars,
       ...pageVars,
@@ -156,6 +158,15 @@ export class PageData {
     return this.workerFiles
   }
 
+  /**
+   * Derive the canonical URL path for this page from its filesystem path and output name.
+   * Index pages get a trailing-slash URL; other outputs include the filename.
+   * @return {string}
+   */
+  #computePageUrl () {
+    return computePageUrl(this.pageInfo)
+  }
+
   /**
    * [init description]
    * @param  {object} params - Parameters required to initialize
diff --git a/lib/build-pages/page-data.test.js b/lib/build-pages/page-data.test.js
new file mode 100644
index 0000000..3daf573
--- /dev/null
+++ b/lib/build-pages/page-data.test.js
@@ -0,0 +1,21 @@
+import { test } from 'node:test'
+import assert from 'node:assert'
+import { computePageUrl } from './compute-page-url.js'
+
+test.describe('computePageUrl', () => {
+  test('root index.html maps to /', () => {
+    assert.strictEqual(computePageUrl({ path: '', outputName: 'index.html' }), '/')
+  })
+
+  test('nested index.html gets a trailing-slash URL', () => {
+    assert.strictEqual(computePageUrl({ path: 'blog/post', outputName: 'index.html' }), '/blog/post/')
+  })
+
+  test('non-index output includes filename in URL', () => {
+    assert.strictEqual(computePageUrl({ path: 'md-page', outputName: 'loose-md.html' }), '/md-page/loose-md.html')
+  })
+
+  test('non-index file at root includes filename only', () => {
+    assert.strictEqual(computePageUrl({ path: '', outputName: 'robots.txt' }), '/robots.txt')
+  })
+})