diff --git a/r2/r2/controllers/promotecontroller.py b/r2/r2/controllers/promotecontroller.py
index 33b8a6ef2..8dea96f77 100644
--- a/r2/r2/controllers/promotecontroller.py
+++ b/r2/r2/controllers/promotecontroller.py
@@ -372,7 +372,7 @@ class PromoteController(ListingController):
         billable_impressions = promote.get_billable_impressions(campaign)
         billable_amount = promote.get_billable_amount(campaign,
                                                       billable_impressions)
-        refund_amount = campaign.bid - billable_amount
+        refund_amount = promote.get_refund_amount(campaign, billable_amount)
         if refund_amount > 0:
             promote.refund_campaign(link, campaign, billable_amount,
                                     billable_impressions)
diff --git a/r2/r2/lib/pages/pages.py b/r2/r2/lib/pages/pages.py
index 42566a427..60e60dce3 100755
--- a/r2/r2/lib/pages/pages.py
+++ b/r2/r2/lib/pages/pages.py
@@ -3481,7 +3481,7 @@ class RefundPage(Reddit):
         billable_impressions = promote.get_billable_impressions(campaign)
         billable_amount = promote.get_billable_amount(campaign,
                                                       billable_impressions)
-        refund_amount = campaign.bid - billable_amount
+        refund_amount = promote.get_refund_amount(campaign, billable_amount)
         self.billable_impressions = billable_impressions
         self.billable_amount = billable_amount
         self.refund_amount = refund_amount
diff --git a/r2/r2/lib/promote.py b/r2/r2/lib/promote.py
index 76e376325..a2486fbe5 100644
--- a/r2/r2/lib/promote.py
+++ b/r2/r2/lib/promote.py
@@ -24,6 +24,7 @@ from __future__ import with_statement
 
 from collections import defaultdict, OrderedDict, namedtuple
 from datetime import datetime, timedelta
+from decimal import Decimal, ROUND_UP
 import itertools
 import json
 import math
@@ -838,8 +839,20 @@ def finalize_completed_campaigns(daysago=1):
             set_underdelivered_campaigns(underdelivered_campaigns)
 
 
+def get_refund_amount(camp, billable):
+    existing_refund = getattr(camp, 'refund_amount', 0.)
+    charge = camp.bid - existing_refund
+    refund_amount = charge - billable
+    refund_amount = Decimal(refund_amount).quantize(Decimal('.01'),
+                                                    rounding=ROUND_UP)
+    return max(float(refund_amount), 0.)
+
+
 def refund_campaign(link, camp, billable_amount, billable_impressions):
-    refund_amount = camp.bid - billable_amount
+    refund_amount = get_refund_amount(camp, billable_amount)
+    if refund_amount <= 0:
+        return
+
     owner = Account._byID(camp.owner_id, data=True)
     try:
         success = authorize.refund_transaction(owner, camp.trans_id,