diff --git a/flashcards/migrations/0018_flashcard_score.py b/flashcards/migrations/0018_flashcard_score.py
new file mode 100644
index 0000000..23714c2
--- /dev/null
+++ b/flashcards/migrations/0018_flashcard_score.py
@@ -0,0 +1,43 @@
+# -*- coding: utf-8 -*-
+from __future__ import unicode_literals
+from math import log1p, exp
+
+from django.db import models, migrations
+from django.utils.timezone import make_aware
+
+
+def update_scores(apps, schema_editor):
+    Flashcard = apps.get_model("flashcards", "Flashcard")
+    for card in Flashcard.objects.all():
+        def seconds_since_epoch(dt):
+            from datetime import datetime
+
+            epoch = make_aware(datetime.utcfromtimestamp(0))
+            delta = dt - epoch
+            return delta.total_seconds()
+
+        z = 0
+        rate = 1.0 / 3600
+        for vote in card.userflashcard_set.iterator():
+            t = seconds_since_epoch(vote.pulled)
+            u = max(z, rate * t)
+            v = min(z, rate * t)
+            z = u + log1p(exp(v - u))
+        card.score = z
+        card.save()
+
+
+class Migration(migrations.Migration):
+    dependencies = [
+        ('flashcards', '0017_auto_20150601_2001'),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name='flashcard',
+            name='score',
+            field=models.FloatField(default=0),
+            preserve_default=False,
+        ),
+        migrations.RunPython(update_scores),
+    ]
diff --git a/flashcards/models.py b/flashcards/models.py
index 36aa465..379b554 100644
--- a/flashcards/models.py
+++ b/flashcards/models.py
@@ -7,7 +7,7 @@ from django.contrib.auth.models import AbstractUser, UserManager
 from django.contrib.auth.tokens import default_token_generator
 from django.core.cache import cache
 from django.core.exceptions import ValidationError
-from django.core.exceptions import PermissionDenied, SuspiciousOperation
+from django.core.exceptions import PermissionDenied
 from django.core.mail import send_mail
 from django.core.validators import MinLengthValidator
 from django.db import IntegrityError
@@ -23,6 +23,8 @@ from cached_property import cached_property
 
 
 
+
+
 # Hack to fix AbstractUser before subclassing it
 
 AbstractUser._meta.get_field('email')._unique = True
@@ -127,6 +129,8 @@ class User(AbstractUser, SimpleEmailConfirmationUserMixin):
         except IntegrityError:
             raise FlashcardAlreadyPulledException()
 
+        flashcard.refresh_score()
+
         import flashcards.pushes
 
         flashcards.pushes.push_feed_event('score_change', flashcard)
@@ -135,13 +139,14 @@ class User(AbstractUser, SimpleEmailConfirmationUserMixin):
     def unpull(self, flashcard):
         if not self.is_in_section(flashcard.section):
             raise ValueError("User not in the section this flashcard belongs to")
-
         try:
             user_card = UserFlashcard.objects.get(user=self, flashcard=flashcard)
         except UserFlashcard.DoesNotExist:
             raise FlashcardNotInDeckException()
         user_card.delete()
 
+        flashcard.refresh_score()
+
         import flashcards.pushes
 
         flashcards.pushes.push_feed_event('score_change', flashcard)
@@ -271,6 +276,7 @@ class Flashcard(Model):
     material_date = DateTimeField(default=now, help_text="The date with which the card is associated")
     previous = ForeignKey('Flashcard', null=True, blank=True, default=None,
                           help_text="The previous version of this card, if one exists")
+    score = FloatField(default=0)
     author = ForeignKey(User)
     is_hidden = BooleanField(default=False)
     hide_reason = CharField(blank=True, null=True, max_length=255, default='',
@@ -284,6 +290,10 @@ class Flashcard(Model):
     def __unicode__(self):
         return u'<flashcard: %s>' % self.text
 
+    def refresh_score(self):
+        self.score = self.calculate_score
+        self.save()
+
     @classmethod
     def push(cls, **kwargs):
         card = cls(**kwargs)
@@ -311,16 +321,6 @@ class Flashcard(Model):
     def is_in_deck(self, user):
         return self.userflashcard_set.filter(user=user).exists()
 
-    def add_to_deck(self, user):
-        if not user.is_in_section(self.section):
-            raise PermissionDenied("You don't have the permission to add this card")
-        try:
-            user_flashcard = UserFlashcard.objects.create(user=user, flashcard=self, mask=self.mask)
-        except IntegrityError:
-            raise SuspiciousOperation("The flashcard is already in the user's deck")
-        user_flashcard.save()
-        return user_flashcard
-
     def edit(self, user, new_data):
         """
         Creates a new flashcard if a new flashcard should be created when the given user edits this flashcard.
@@ -347,7 +347,7 @@ class Flashcard(Model):
             self.pk = None
             self.mask = new_data.get('mask', self.mask)
             self.save()
-            self.add_to_deck(user)
+            user.pull(self)
         else:
             user_card, created = UserFlashcard.objects.get_or_create(user=user, flashcard=self)
             user_card.mask = new_data.get('mask', user_card.mask)
@@ -372,7 +372,7 @@ class Flashcard(Model):
         hide.delete()
 
     @cached_property
-    def score(self):
+    def calculate_score(self):
         def seconds_since_epoch(dt):
             from datetime import datetime
 
@@ -526,8 +526,7 @@ class Section(Model):
         return '%s %s' % (self.department_abbreviation, self.course_num)
 
     def get_feed_for_user(self, user, page=1):
-        cards = list(self.get_cards_for_user(user)[(page - 1) * self.PAGE_SIZE:page * self.PAGE_SIZE])
-        cards.sort(key=lambda x: -x.score)
+        cards = self.get_cards_for_user(user).order_by('-score')[(page - 1) * self.PAGE_SIZE:page * self.PAGE_SIZE]
         return cards
 
     def get_cards_for_user(self, user):