diff --git a/content.py b/content.py
index 36338d2..9fba2b9 100644
--- a/content.py
+++ b/content.py
@@ -133,17 +133,9 @@ def _range_bar(low_f, high_f) -> dict | None:
 
 
 def _ordinal(n) -> str:
-    """96 -> '96th'. Percentiles read as ordinals in prose ('in the 96th
-    percentile'), and the frontend's shared.js ord() does the same client-side."""
-    try:
-        i = int(round(float(n)))
-    except (TypeError, ValueError):
-        return "—"
-    if 10 <= i % 100 <= 20:
-        suffix = "th"
-    else:
-        suffix = {1: "st", 2: "nd", 3: "rd"}.get(i % 10, "th")
-    return f"{i}{suffix}"
+    """Percentile -> display ordinal. Delegates to grading so every surface
+    (Day page, calendar, chart, city pages, homepage strip) agrees."""
+    return grading.pct_ordinal(n)
 
 
 _env.globals["temp_class"] = temp_class
diff --git a/grading.py b/grading.py
index 39fb5d7..b47008c 100644
--- a/grading.py
+++ b/grading.py
@@ -8,6 +8,8 @@ empirical percentile and mapped to a human-readable grade.
 import datetime
 import warnings
 
+import math
+
 import numpy as np
 import polars as pl
 
@@ -82,6 +84,29 @@ _TEMP_LADDER = _ladder_from(TEMP_BANDS)
 _RAIN_LADDER = _ladder_from(RAIN_BANDS, bottom_lo=0)
 
 
+def pct_ordinal(pct) -> str:
+    """A percentile as a display ordinal: 66.4 -> '66th', 99.6 -> '99th'.
+
+    Floored into 1..99 on purpose. An empirical percentile is a rank against the
+    sample, so rounding can land on 100 (or 0), and "100th percentile" reads as a
+    measurement error rather than "as extreme as it has ever been". The band label
+    ("Near Record") carries the how-extreme part.
+
+    Canonical for every surface — the frontend mirrors it as pctOrd() in
+    shared.js, so the Day page, the calendar tooltip, the chart, the city pages
+    and the homepage strip all say the same thing about the same reading.
+    """
+    try:
+        # floor(x + 0.5), NOT round(): Python's round() is half-to-even, so it
+        # gives 16 for 16.5 while JavaScript's Math.round gives 17 — the same
+        # reading would then read "16th" server-side and "17th" client-side.
+        n = min(99, max(1, math.floor(float(pct) + 0.5)))
+    except (TypeError, ValueError):
+        return "—"
+    suffix = "th" if 10 <= n % 100 <= 20 else {1: "st", 2: "nd", 3: "rd"}.get(n % 10, "th")
+    return f"{n}{suffix}"
+
+
 def _band(pct: float, bands) -> tuple[str, str]:
     # The top tier is strict (pct > its threshold): "Near Record" high means
     # strictly beyond the 99th percentile — the top <1% — mirroring the
diff --git a/homepage.py b/homepage.py
index f729039..a38205f 100644
--- a/homepage.py
+++ b/homepage.py
@@ -96,16 +96,8 @@ def _short_date(date_s: str) -> str:
 
 
 def _pct_label(pct: float) -> str:
-    """A percentile as an ordinal, clamped to 1..99.
-
-    An empirical percentile can round to 100 (or 0), and "100th percentile" reads
-    as a measurement error rather than "as hot as it has ever been". Flooring into
-    the real 1-99 range keeps it honest — the value and the band label carry the
-    "how extreme" part anyway.
-    """
-    n = min(99, max(1, int(round(pct))))
-    suffix = "th" if 10 <= n % 100 <= 20 else {1: "st", 2: "nd", 3: "rd"}.get(n % 10, "th")
-    return f"{n}{suffix}"
+    """Kept as a name the feed builder reads; the rule itself lives in grading."""
+    return grading.pct_ordinal(pct)
 
 
 def _grade_label(grade: str | None, tail: str) -> str:
diff --git a/templates/city.html.j2 b/templates/city.html.j2
index dcbf276..5eee6ed 100644
--- a/templates/city.html.j2
+++ b/templates/city.html.j2
@@ -31,7 +31,7 @@
       <div class="today-card" style="border-left-color: var(--{{ c.cls }})">
         <span class="tc-label">{{ c.label }}</span>
         <span class="tc-value">{{ c.value }}</span>
-        {% if c.percentile is not none %}<span class="tc-grade">{{ c.grade }} · {{ c.percentile }}th pct</span>
+        {% if c.percentile is not none %}<span class="tc-grade">{{ c.grade }} · {{ c.percentile|ordinal }} pct</span>
         {% else %}<span class="tc-grade">{{ c.grade }}</span>{% endif %}
       </div>
       {% endfor %}
diff --git a/tests/test_content.py b/tests/test_content.py
index e0f3eb7..bf9dbb1 100644
--- a/tests/test_content.py
+++ b/tests/test_content.py
@@ -1,12 +1,15 @@
 """Tests for the crawlable SEO content pages: the city set, robots/sitemap, and
 that the server-rendered pages contain the stats in the HTML (with the weather
 layer faked, like test_api.py)."""
+import re
+
 import pytest
 from fastapi.testclient import TestClient
 
 import app as appmod
 import cities
 import climate
+import grading
 
 # BASE defaults to /thermograph in tests (THERMOGRAPH_BASE unset).
 B = "/thermograph"
@@ -289,3 +292,31 @@ def test_brand_lockup_links_home(client, path):
     assert href in ("./", f"{B}/"), f"{path}: brand links to {href!r}, not home"
     assert '<span class="logo">' in head.split("<a href=", 1)[1], \
         f"{path}: the mark sits outside the home link"
+
+
+# Percentiles are shown on the Day page, the calendar tooltip, the chart, the
+# city pages and the homepage strip. They all have to say the same thing about
+# the same reading, so the rule lives in grading.pct_ordinal() and every surface
+# defers to it (the frontend mirrors it as pctOrd in shared.js).
+def test_pct_ordinal_rule():
+    assert grading.pct_ordinal(66.4) == "66th"
+    assert grading.pct_ordinal(1.2) == "1st"
+    assert grading.pct_ordinal(22) == "22nd"
+    assert grading.pct_ordinal(3) == "3rd"
+    assert grading.pct_ordinal(11) == "11th"
+    # Floored into 1..99: an empirical percentile is a rank against the sample,
+    # so "100th percentile" reads as a measurement error.
+    assert grading.pct_ordinal(99.6) == "99th"
+    assert grading.pct_ordinal(100) == "99th"
+    assert grading.pct_ordinal(0) == "1st"
+    assert grading.pct_ordinal(None) == "—"
+
+
+def test_city_page_percentiles_are_real_ordinals(client):
+    """The city page used to render `{{ c.percentile }}th pct` against a float,
+    producing "97.1th pct" and "1th pct" on every one of the ~1000 city pages."""
+    html = client.get(f"{B}/climate/{SLUG}").text
+    assert "th pct" in html or "st pct" in html or "nd pct" in html or "rd pct" in html
+    # No float ordinals, no impossible ones, no "1th"/"2th"/"3th".
+    for bad in re.findall(r"\d+\.\d+(?:st|nd|rd|th)|100th|\b0th|\b\d*[123]th", html):
+        raise AssertionError(f"malformed percentile ordinal: {bad!r}")