diff --git a/aleksis/apps/chronos/models.py b/aleksis/apps/chronos/models.py
index 332acc7c380b15cf7b85b4a1eee5d71a6dd7c889..c975925748e2cad62aa3ee8d958c0f3e2fb71b0b 100644
--- a/aleksis/apps/chronos/models.py
+++ b/aleksis/apps/chronos/models.py
@@ -10,10 +10,12 @@ from django.db.models import F, Q
 from django.http.request import QueryDict
 from django.utils.translation import ugettext_lazy as _
 
+from calendarweek.django import CalendarWeek, i18n_day_names_lazy, i18n_day_abbrs_lazy
+
 from aleksis.core.mixins import ExtensibleModel
 from aleksis.core.models import Group, Person
 
-from .util import CalendarWeek, week_weekday_from_date
+from .util import week_weekday_from_date
 
 
 class LessonPeriodManager(models.Manager):
@@ -203,25 +205,8 @@ class LessonSubstitutionQuerySet(LessonDataQuerySet):
 
 
 class TimePeriod(models.Model):
-    WEEKDAY_CHOICES = [
-        (0, _("Sunday")),
-        (1, _("Monday")),
-        (2, _("Tuesday")),
-        (3, _("Wednesday")),
-        (4, _("Thursday")),
-        (5, _("Friday")),
-        (6, _("Saturday")),
-    ]
-
-    WEEKDAY_CHOICES_SHORT = [
-        (0, _("Sun")),
-        (1, _("Mon")),
-        (2, _("Tue")),
-        (3, _("Wed")),
-        (4, _("Thu")),
-        (5, _("Fri")),
-        (6, _("Sat")),
-    ]
+    WEEKDAY_CHOICES = i18n_day_names_lazy()
+    WEEKDAY_CHOICES_SHORT = i18n_day_abbrs_lazy()
 
     weekday = models.PositiveSmallIntegerField(verbose_name=_("Week day"), choices=WEEKDAY_CHOICES)
     period = models.PositiveSmallIntegerField(verbose_name=_("Number of period"))
diff --git a/aleksis/apps/chronos/util.py b/aleksis/apps/chronos/util.py
index 5af26ed14b1cf83507a853728a595bb6caff1a9d..6e49d8753d1348aed3a270cf8072484806e51cf4 100644
--- a/aleksis/apps/chronos/util.py
+++ b/aleksis/apps/chronos/util.py
@@ -1,97 +1,7 @@
-from __future__ import annotations
+from datetime import date
+from typing import Tuple, List
 
-from dataclasses import dataclass
-from datetime import date, datetime, timedelta
-from typing import Optional, Sequence, Tuple, Union, List
-
-from django.apps import apps
-from django.db import models
-from django.utils.translation import ugettext as _
-
-
-@dataclass
-class CalendarWeek:
-    """ A calendar week defined by year and ISO week number. """
-
-    year: Optional[int] = None
-    week: Optional[int] = None
-
-    @classmethod
-    def from_date(cls, when: date):
-        """ Get the calendar week by a date object (the week this date is in). """
-
-        week = int(when.strftime("%V"))
-        year = when.year + 1 if when.month == 12 and week == 1 else when.year
-
-        return cls(year=year, week=week)
-
-    @classmethod
-    def current_week(cls) -> int:
-        """ Get the current week number. """
-
-        return cls().week
-
-    @classmethod
-    def weeks_within(cls, start: date, end: date) -> Sequence[CalendarWeek]:
-        """ Get all calendar weeks within a date range. """
-
-        if start > end:
-            raise ValueError("End date must be after start date.")
-
-        current = start
-        weeks = []
-        while current < end:
-            weeks.append(cls.from_date(current))
-            current += timedelta(days=7)
-
-        return weeks
-
-    def __post_init__(self) -> None:
-        today = date.today()
-
-        if not self.year:
-            self.year = today.year
-        if not self.week:
-            self.week = int(today.strftime("%V"))
-
-    def __str__(self) -> str:
-        return "%s %d (%s %s %s)" % (_("Calendar Week"), self.week, self[0], _("to"), self[-1],)
-
-    def __len__(self) -> int:
-        return 7
-
-    def __getitem__(self, n: int) -> date:
-        if n < -7 or n > 6:
-            raise IndexError("Week day %d is out of range." % n)
-
-        if n < 0:
-            n += 7
-
-        return datetime.strptime("%d-%d-%d" % (self.year, self.week, n + 1), "%G-%V-%u").date()
-
-    def __contains__(self, day: date) -> bool:
-        return self.__class__.form_date(day) == self
-
-    def __eq__(self, other: CalendarWeek) -> bool:
-        return self.year == other.year and self.week == other.week
-
-    def __lt__(self, other: CalendarWeek) -> bool:
-        return self[0] < other[0]
-
-    def __gt__(self, other: CalendarWeek) -> bool:
-        return self[0] > other[0]
-
-    def __le__(self, other: CalendarWeek) -> bool:
-        return self[0] <= other[0]
-
-    def __gr__(self, other: CalendarWeek) -> bool:
-        return self[0] >= other[0]
-
-    def __add__(self, weeks: int) -> CalendarWeek:
-        return self.__class__.from_date(self[0] + timedelta(days=weeks * 7))
-
-    def __sub__(self, weeks: int) -> CalendarWeek:
-        return self.__class__.from_date(self[0] - timedelta(days=weeks * 7))
+from calendarweek import CalendarWeek
 
 
 def week_weekday_from_date(when: date) -> Tuple[CalendarWeek, int]:
diff --git a/pyproject.toml b/pyproject.toml
index 9065066e24063dde8042828c88bc814afc7fa639..79c3be725b3dcd43000db33821fc601170f539d3 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -20,6 +20,7 @@ classifiers = [
 
 [tool.poetry.dependencies]
 python = "^3.7"
+calendarweek = "^0.1"
 AlekSIS = { path = "../../.." }
 
 [build-system]