diff --git a/tildes/static/js/behaviors/comment-reply-button.js b/tildes/static/js/behaviors/comment-reply-button.js
index f09f969..32214dc 100644
--- a/tildes/static/js/behaviors/comment-reply-button.js
+++ b/tildes/static/js/behaviors/comment-reply-button.js
@@ -79,21 +79,17 @@ $.onmount("[data-js-comment-reply-button]", function() {
             }
         }
 
-        var parentCommentTimestamp = new Date(
-            $parentComment
-                .find(".comment-posted-time")
-                .first()
-                .attr("datetime")
-        );
-
-        // add a warning if the comment being replied to is over a week old
-        if (Date.now() - parentCommentTimestamp > 1000 * 3600 * 24 * 7) {
+        // add a warning about the comment's age, if necessary (determined by backend)
+        var warningAge = $(this).attr("data-js-old-warning-age");
+        if (warningAge) {
             var warningDiv = document.createElement("div");
             warningDiv.classList.add("warning-old-reply");
             warningDiv.innerHTML =
                 '<p class="text-warning text-small">The comment you\'re replying to ' +
-                "is over a week old. Replying to old comments is fine as long as " +
-                "you're contributing to the discussion.</p>";
+                "is " +
+                warningAge +
+                " old. Replying to old comments is fine as long as you're " +
+                "contributing to the discussion.</p>";
             clone.querySelector("form").prepend(warningDiv);
         }
 
diff --git a/tildes/tildes/jinja.py b/tildes/tildes/jinja.py
index b881e3a..2065dcf 100644
--- a/tildes/tildes/jinja.py
+++ b/tildes/tildes/jinja.py
@@ -8,7 +8,11 @@ from urllib.parse import quote_plus
 
 from pyramid.config import Configurator
 
-from tildes.lib.datetime import adaptive_date, descriptive_timedelta
+from tildes.lib.datetime import (
+    adaptive_date,
+    descriptive_timedelta,
+    vague_timedelta_description,
+)
 from tildes.models.comment import Comment
 from tildes.models.group import Group
 from tildes.models.topic import Topic
@@ -46,6 +50,7 @@ def includeme(config: Configurator) -> None:
         "adaptive_date": adaptive_date,
         "ago": descriptive_timedelta,
         "quote_plus": do_quote_plus,
+        "vague_timedelta_description": vague_timedelta_description,
     }
 
     # add custom jinja tests
diff --git a/tildes/tildes/lib/datetime.py b/tildes/tildes/lib/datetime.py
index ec4863f..2d0f332 100644
--- a/tildes/tildes/lib/datetime.py
+++ b/tildes/tildes/lib/datetime.py
@@ -137,6 +137,36 @@ def descriptive_timedelta(
     return result
 
 
+def vague_timedelta_description(delta: timedelta) -> str:
+    """Vaguely describe how long a timedelta refers to, like "over 2 weeks"."""
+    if delta.days < 1:
+        raise ValueError("The timedelta must be at least a day.")
+
+    day_thresholds = {
+        "year": 365,
+        "month": 30,
+        "week": 7,
+        "day": 1,
+    }
+
+    for threshold, days in day_thresholds.items():
+        if delta.days >= days:
+            largest_threshold = threshold
+            break
+
+    count = str(delta.days // day_thresholds[largest_threshold])
+
+    # set the strings we'll output based on count - change count of 1 to "a", otherwise
+    # pluralize the threshold name (e.g. change "week" to "weeks")
+    if count == "1":
+        count = "a"
+        period = largest_threshold
+    else:
+        period = largest_threshold + "s"
+
+    return f"over {count} {period}"
+
+
 def adaptive_date(
     target: datetime, abbreviate: bool = False, precision: Optional[int] = None
 ) -> str:
diff --git a/tildes/tildes/templates/macros/comments.jinja2 b/tildes/tildes/templates/macros/comments.jinja2
index 8944ca4..aa1b89a 100644
--- a/tildes/tildes/templates/macros/comments.jinja2
+++ b/tildes/tildes/templates/macros/comments.jinja2
@@ -212,7 +212,16 @@
         {% endif %}
 
         {% if request.has_permission('reply', comment) %}
-          <li><button class="btn-post-action" name="reply" data-js-comment-reply-button>Reply</button></li>
+          <li>
+            <button
+              class="btn-post-action"
+              name="reply"
+              data-js-comment-reply-button
+              {% if comment.age.days >= 7 %}
+              data-js-old-warning-age="{{ comment.age|vague_timedelta_description }}"
+              {% endif %}
+            >Reply</button>
+          </li>
         {% endif %}
       </menu>
     {% endif %}
diff --git a/tildes/tildes/templates/topic.jinja2 b/tildes/tildes/templates/topic.jinja2
index fd07a7d..36c2f90 100644
--- a/tildes/tildes/templates/topic.jinja2
+++ b/tildes/tildes/templates/topic.jinja2
@@ -227,9 +227,9 @@
       data-js-prevent-double-submit
       data-js-confirm-leave-page-unsaved
     >
-      {% if old_topic_warning %}
+      {% if topic.age.days >= 7 %}
       <div class="warning-old-reply">
-        <p class="text-warning text-small">This topic is over a week old. Replying to old topics is fine as long as you're contributing to the discussion.</p>
+        <p class="text-warning text-small">This topic is {{ topic.age|vague_timedelta_description }} old. Replying to old topics is fine as long as you're contributing to the discussion.</p>
       </div>
       {% endif %}
       <input type="hidden" name="csrf_token" value="{{ get_csrf_token() }}">
diff --git a/tildes/tildes/views/topic.py b/tildes/tildes/views/topic.py
index d62ee34..3d9c028 100644
--- a/tildes/tildes/views/topic.py
+++ b/tildes/tildes/views/topic.py
@@ -7,7 +7,6 @@ from collections import namedtuple
 from decimal import Decimal
 from typing import Any, Dict, Optional, Union
 
-from datetime import timedelta
 from marshmallow import missing, ValidationError
 from marshmallow.fields import Boolean, String
 from pyramid.httpexceptions import HTTPFound
@@ -422,8 +421,6 @@ def get_topic(request: Request, comment_order: CommentTreeSortOption) -> dict:
             tree.uncollapse_new_comments(topic.last_visit_time)
             tree.finalize_collapsing_maximized()
 
-    old_topic_warning = topic.age > timedelta(days=7)
-
     return {
         "topic": topic,
         "log": log,
@@ -431,7 +428,6 @@ def get_topic(request: Request, comment_order: CommentTreeSortOption) -> dict:
         "comment_order": comment_order,
         "comment_order_options": CommentTreeSortOption,
         "comment_label_options": CommentLabelOption,
-        "old_topic_warning": old_topic_warning,
     }