diff --git a/pinaxcon/templatetags/nbpy_tags.py b/pinaxcon/templatetags/nbpy_tags.py
new file mode 100644
index 0000000000000000000000000000000000000000..16af7568bad8cef98121d1c661f82d59c9f43498
--- /dev/null
+++ b/pinaxcon/templatetags/nbpy_tags.py
@@ -0,0 +1,44 @@
+from registrasion.models import commerce
+from registrasion.controllers.category import CategoryController
+from registrasion.controllers.item import ItemController
+
+from decimal import Decimal
+from django import template
+from django.conf import settings
+from django.db.models import Sum
+from urllib import urlencode  # TODO: s/urllib/six.moves.urllib/
+
+register = template.Library()
+
+
+@register.simple_tag(takes_context=True)
+def donation_income(context, invoice):
+    ''' Calculates the donation income for a given invoice.
+
+    Returns:
+        the donation income.
+
+    '''
+
+    # 15% (FSA) goes to Conservancy; 85% is real goods
+
+    fsa_rate = Decimal("0.85")
+    rbi_full_ticket = Decimal("68.00")
+    rbi_early_bird_discount = Decimal("-21.35")
+    rbi = []
+
+    for line in invoice.lineitem_set.all():
+        if line.product.category.name == "Ticket":
+            if line.product.name.startswith("Unaffiliated Individual"):
+                # Includes full price & discounts
+                rbi.append(line.total_price * fsa_rate)
+            else:
+                if line.total_price > 0:
+                    rbi.append(rbi_full_ticket)
+                elif line.total_price < 0:
+                    rbi.append(rbi_early_bird_discount)
+        elif line.product.category.name == "T-Shirt":
+            rbi.append(line.total_price * fsa_rate)
+
+    donation = (invoice.value - sum(rbi))
+    return donation.quantize(Decimal('.01'))