diff --git a/conservancy/news/templatetags/subtract.py b/conservancy/news/templatetags/subtract.py
new file mode 100644
index 0000000000000000000000000000000000000000..111daffc204528f3b78a589c3c8ed3f81ca1185a
--- /dev/null
+++ b/conservancy/news/templatetags/subtract.py
@@ -0,0 +1,7 @@
+from django import template
+
+register = template.Library()
+
+@register.filter
+def subtract(value, arg):
+    return value - arg