diff --git a/RIGS/finance.py b/RIGS/finance.py
index fb075684..20199f0a 100644
--- a/RIGS/finance.py
+++ b/RIGS/finance.py
@@ -13,13 +13,20 @@ class InvoiceIndex(generic.ListView):
     template_name = 'RIGS/invoice_list.html'
 
     def get_queryset(self):
-        active = self.model.objects.filter(void=False).select_related('payment_set', 'event').prefetch_related(
-            'event__items').defer('event__person', 'event__organisation', 'event__venue', 'event__mic')
-        set = []
-        for invoice in active:
-            if invoice.balance != 0:
-                set.append(invoice)
-        return set
+        # Manual query is the only way I have found to do this efficiently. Not ideal but needs must
+        query = self.model.objects.raw(
+            "SELECT *, "
+            "(SELECT SUM(ei.cost * ei.quantity) FROM RIGS_eventitem AS ei WHERE ei.event_id = i.event_id) AS cost, "
+            "(SELECT SUM(p.amount) FROM RIGS_payment AS p WHERE p.invoice_id = i.id) AS payments FROM RIGS_invoice as i "
+            "HAVING (cost - payments) > 0;"
+        )
+
+        items = []
+
+        for invoice in query:
+            items.append(invoice)
+
+        return query
 
 
 class InvoiceDetail(generic.DetailView):
diff --git a/RIGS/models.py b/RIGS/models.py
index da58bbc6..de1156b7 100644
--- a/RIGS/models.py
+++ b/RIGS/models.py
@@ -247,10 +247,11 @@ class Event(models.Model, RevisionMixin):
     """
     @property
     def sum_total(self):
-        total = 0
-        for item in self.items.filter(cost__gt=0):
-            total += item.total_cost
-        return total
+        # Manual querying is required for efficiency whilst maintaining floating point arithmetic
+        total = self.items.raw("SELECT id, SUM(quantity * cost) AS sum_total FROM RIGS_eventitem WHERE event_id=%i" % self.id)[0]
+        if total.sum_total:
+            return total.sum_total
+        return 0.0
 
     @cached_property
     def vat_rate(self):
@@ -329,16 +330,15 @@ class Invoice(models.Model):
 
     @property
     def payment_total(self):
-        sum = self.payment_set.aggregate(models.Sum('amount'))['amount__sum']
-        # for payment in self.payment_set.all():
-        #     total += payment.amount
-        if sum:
-            return sum
-        return 0
+        # Manual querying is required for efficiency whilst maintaining floating point arithmetic
+        total = self.payment_set.raw("SELECT id, SUM(amount) AS total FROM RIGS_payment WHERE invoice_id=%i" % self.id)[0]
+        if total.total:
+            return total.total
+        return 0.0
 
     @property
     def balance(self):
-        return self.sum_total - self.payment_total
+        return float(self.sum_total) - float(self.payment_total)
 
     def __str__(self):
         return "%i: %s (%.2f)" % (self.pk, self.event, self.balance)