diff --git a/accounting/templates/accounting/cash.html b/accounting/templates/accounting/cash.html
index cbefa9f..d7efe21 100644
--- a/accounting/templates/accounting/cash.html
+++ b/accounting/templates/accounting/cash.html
@@ -73,13 +73,13 @@ First written: 2020/7/1
     <div class="dropdown-menu account-picker">
       <div class="dropdown-header">{% trans "Shortcuts" context "Accounting|Account|" as text %}{{ text|force_escape }}</div>
       {% for account in shortcut_accounts %}
-        <a class="dropdown-item {% if account.code == current_account.code %} active {% endif %}>" href="{% url "accounting:cash" account.code period.spec %}">
+        <a class="dropdown-item {% if account.code == current_account.code %} active {% endif %}>" href="{% url "accounting:cash" account.code period %}">
           {{ account.title|title }}
         </a>
       {% endfor %}
       <div class="dropdown-header">{% trans "All" context "Accounting|Account|" as text %}{{ text|force_escape }}</div>
       {% for account in all_accounts %}
-        <a class="dropdown-item {% if account.code == current_account.code %} active {% endif %}>" href="{% url "accounting:cash" account.code period.spec %}">
+        <a class="dropdown-item {% if account.code == current_account.code %} active {% endif %}>" href="{% url "accounting:cash" account.code period %}">
           {{ account.code }} {{ account.title|title }}
         </a>
       {% endfor %}
diff --git a/accounting/templates/accounting/income-statement.html b/accounting/templates/accounting/income-statement.html
index b77742b..50b3c24 100644
--- a/accounting/templates/accounting/income-statement.html
+++ b/accounting/templates/accounting/income-statement.html
@@ -112,7 +112,7 @@ First written: 2020/7/19
                     <td class="amount {% if item.balance < 0 %} text-danger {% endif %}">{{ item.balance|accounting_amount }}</td>
                     <td class="amount"></td>
                     <td class="actions">
-                      <a href="{% url "accounting:ledger" item.code period.spec %}" class="btn btn-info" role="button">
+                      <a href="{% url "accounting:ledger" item.code period %}" class="btn btn-info" role="button">
                         <i class="fas fa-eye"></i>
                         <span class="d-none d-lg-inline">{% trans "View" context "Accounting|" as text %}{{ text|force_escape }}</span>
                       </a>
@@ -172,7 +172,7 @@ First written: 2020/7/19
               </li>
               {% for item in group.details %}
                 <li class="list-group-item d-flex justify-content-between align-items-center account">
-                  <a class="list-group-item-action" href="{% url "accounting:ledger" item.code period.spec %}">
+                  <a class="list-group-item-action" href="{% url "accounting:ledger" item.code period %}">
                     {{ item.title|title }}
                     <div class="float-right">
                       <span class="badge {% if item.balance < 0 %} badge-warning {% else %} badge-secondary {% endif %} badge-pill">
diff --git a/accounting/templates/accounting/ledger.html b/accounting/templates/accounting/ledger.html
index 26f519f..3ec5a79 100644
--- a/accounting/templates/accounting/ledger.html
+++ b/accounting/templates/accounting/ledger.html
@@ -72,7 +72,7 @@ First written: 2020/7/16
     </button>
     <div class="dropdown-menu account-picker">
       {% for account in accounts %}
-        <a class="dropdown-item {% if account.code == current_account.code %} active {% endif %}" href="{% url "accounting:ledger" account.code period.spec %}">
+        <a class="dropdown-item {% if account.code == current_account.code %} active {% endif %}" href="{% url "accounting:ledger" account.code period %}">
           {{ account.code }} {{ account.title|title }}
         </a>
       {% endfor %}
diff --git a/accounting/templates/accounting/trial-balance.html b/accounting/templates/accounting/trial-balance.html
index 6751cf3..7dfefb8 100644
--- a/accounting/templates/accounting/trial-balance.html
+++ b/accounting/templates/accounting/trial-balance.html
@@ -101,7 +101,7 @@ First written: 2020/7/19
                 <td class="amount">{{ item.debit|accounting_amount }}</td>
                 <td class="amount">{{ item.credit|accounting_amount }}</td>
                 <td class="actions">
-                  <a href="{% url "accounting:ledger" item.code period.spec %}" class="btn btn-info" role="button">
+                  <a href="{% url "accounting:ledger" item.code period %}" class="btn btn-info" role="button">
                     <i class="fas fa-eye"></i>
                     <span class="d-none d-lg-inline">{% trans "View" context "Accounting|" as text %}{{ text|force_escape }}</span>
                   </a>
diff --git a/accounting/urls.py b/accounting/urls.py
index b4de7ba..485e7ae 100644
--- a/accounting/urls.py
+++ b/accounting/urls.py
@@ -21,8 +21,10 @@
 
 from django.urls import path, register_converter
 
+from mia_core.period import Period
 from . import views
 from mia_core import views as mia_core_views
+from .models import Transaction
 from .views import reports
 
 
@@ -39,11 +41,50 @@ class TransactionTypeConverter:
 
 register_converter(TransactionTypeConverter, "txn-type")
 
+
+class PeriodConverter:
+    """The path converter for the period."""
+    regex = ".+"
+
+    def to_python(self, value):
+        """Returns the period by the period specification.
+
+        Args:
+            value (str): The period specification.
+
+        Returns:
+            Period: The period.
+        """
+        first_txn = Transaction.objects.order_by("date").first()
+        data_start = first_txn.date if first_txn is not None else None
+        last_txn = Transaction.objects.order_by("-date").first()
+        data_end = last_txn.date if last_txn is not None else None
+        period = Period(value, data_start, data_end)
+        if period.error is not None:
+            raise ValueError
+        return period
+
+    def to_url(self, value):
+        """Returns the specification of a period.
+
+        Args:
+            value (Period|str): The period.
+
+        Returns:
+            str: The period specification.
+        """
+        if isinstance(value, Period):
+            return value.spec
+        return value
+
+
+register_converter(PeriodConverter, "period")
+
 app_name = "accounting"
 urlpatterns = [
     path("", views.home, name="home"),
     path("cash", reports.cash_default, name="cash.home"),
-    path("cash/<str:account_code>/<str:period_spec>",
+    path("cash/<str:account_code>/<period:period>",
          reports.cash, name="cash"),
     path("cash-summary",
          reports.cash_summary_default, name="cash-summary.home"),
@@ -51,7 +92,7 @@ urlpatterns = [
          reports.cash_summary, name="cash-summary"),
     path("ledger",
          reports.ledger_default, name="ledger.home"),
-    path("ledger/<str:account_code>/<str:period_spec>",
+    path("ledger/<str:account_code>/<period:period>",
          reports.ledger, name="ledger"),
     path("ledger-summary",
          reports.ledger_summary_default, name="ledger-summary.home"),
@@ -59,19 +100,19 @@ urlpatterns = [
          reports.ledger_summary, name="ledger-summary"),
     path("journal",
          reports.journal_default, name="journal.home"),
-    path("journal/<str:period_spec>",
+    path("journal/<period:period>",
          reports.journal, name="journal"),
     path("trial-balance",
          reports.trial_balance_default, name="trial-balance.home"),
-    path("trial-balance/<str:period_spec>",
+    path("trial-balance/<period:period>",
          reports.trial_balance, name="trial-balance"),
     path("income-statement",
          reports.income_statement_default, name="income-statement.home"),
-    path("income-statement/<str:period_spec>",
+    path("income-statement/<period:period>",
          reports.income_statement, name="income-statement"),
     path("balance-sheet",
          reports.balance_sheet_default, name="balance-sheet.home"),
-    path("balance-sheet/<str:period_spec>",
+    path("balance-sheet/<period:period>",
          reports.balance_sheet, name="balance-sheet"),
     path("search",
          reports.search, name="search"),
diff --git a/accounting/utils.py b/accounting/utils.py
index 2e8adce..35b8b02 100644
--- a/accounting/utils.py
+++ b/accounting/utils.py
@@ -71,7 +71,7 @@ class ReportUrl:
     def cash(self):
         return reverse(
             "accounting:cash",
-            args=[self._cash_account.code, self._period.spec])
+            args=[self._cash_account.code, self._period])
 
     @property
     def cash_summary(self):
@@ -82,7 +82,7 @@ class ReportUrl:
     def ledger(self):
         return reverse(
             "accounting:ledger",
-            args=[self._ledger_account.code, self._period.spec])
+            args=[self._ledger_account.code, self._period])
 
     @property
     def ledger_summary(self):
@@ -92,19 +92,19 @@ class ReportUrl:
 
     @property
     def journal(self):
-        return reverse("accounting:journal", args=[self._period.spec])
+        return reverse("accounting:journal", args=[self._period])
 
     @property
     def trial_balance(self):
         return reverse(
-            "accounting:trial-balance", args=[self._period.spec])
+            "accounting:trial-balance", args=[self._period])
 
     @property
     def income_statement(self):
         return reverse(
-            "accounting:income-statement", args=[self._period.spec])
+            "accounting:income-statement", args=[self._period])
 
     @property
     def balance_sheet(self):
         return reverse(
-            "accounting:balance-sheet", args=[self._period.spec])
+            "accounting:balance-sheet", args=[self._period])
diff --git a/accounting/views/reports.py b/accounting/views/reports.py
index 7d5ddb7..7b5059b 100644
--- a/accounting/views/reports.py
+++ b/accounting/views/reports.py
@@ -59,19 +59,17 @@ def cash_default(request):
 
 @require_GET
 @digest_login_required
-def cash(request, account_code, period_spec):
+def cash(request, account_code, period):
     """The cash account.
 
     Args:
         request (HttpRequest) The request.
         account_code (str): The code of the specified account.
-        period_spec (str): The period specification.
+        period (Period): The period.
 
     Returns:
         HttpResponse: The response.
     """
-    # The period
-    period = _get_period(period_spec)
     # The account
     accounts = _cash_accounts()
     current_account = None
@@ -295,19 +293,17 @@ def ledger_default(request):
 
 @require_GET
 @digest_login_required
-def ledger(request, account_code, period_spec):
+def ledger(request, account_code, period):
     """The ledger.
 
     Args:
         request (HttpRequest) The request.
         account_code (str): The code of the specified account.
-        period_spec (str): The period specification.
+        period (Period): The period.
 
     Returns:
         HttpResponse: The response.
     """
-    # The period
-    period = _get_period(period_spec)
     # The account
     accounts = _ledger_accounts()
     current_account = None
@@ -458,18 +454,16 @@ def journal_default(request):
 
 @require_GET
 @digest_login_required
-def journal(request, period_spec):
+def journal(request, period):
     """The journal.
 
     Args:
         request (HttpRequest) The request.
-        period_spec (str): The period specification.
+        period (Period): The period.
 
     Returns:
         HttpResponse: The response.
     """
-    # The period
-    period = _get_period(period_spec)
     # The accounting records
     records = Record.objects\
         .filter(
@@ -547,18 +541,16 @@ def trial_balance_default(request):
 
 @require_GET
 @digest_login_required
-def trial_balance(request, period_spec):
+def trial_balance(request, period):
     """The trial balance.
 
     Args:
         request (HttpRequest) The request.
-        period_spec (str): The period specification.
+        period (Period): The period.
 
     Returns:
         HttpResponse: The response.
     """
-    # The period
-    period = _get_period(period_spec)
     # The accounts
     nominal = list(
         Account.objects
@@ -658,18 +650,16 @@ def income_statement_default(request):
 
 @require_GET
 @digest_login_required
-def income_statement(request, period_spec):
+def income_statement(request, period):
     """The income statement.
 
     Args:
         request (HttpRequest) The request.
-        period_spec (str): The period specification.
+        period (Period): The period.
 
     Returns:
         HttpResponse: The response.
     """
-    # The period
-    period = _get_period(period_spec)
     # The accounts
     accounts = list(
         Account.objects
@@ -745,18 +735,16 @@ def balance_sheet_default(request):
 
 @require_GET
 @digest_login_required
-def balance_sheet(request, period_spec):
+def balance_sheet(request, period):
     """The balance sheet.
 
     Args:
         request (HttpRequest) The request.
-        period_spec (str): The period specification.
+        period (Period): The period.
 
     Returns:
         HttpResponse: The response.
     """
-    # The period
-    period = _get_period(period_spec)
     # The accounts
     accounts = list(
         Account.objects
@@ -774,7 +762,7 @@ def balance_sheet(request, period_spec):
         .order_by("code"))
     for account in accounts:
         account.url = reverse(
-            "accounting:ledger", args=[account.code, period.spec])
+            "accounting:ledger", args=(account.code, period))
     balance = Record.objects\
         .filter(
             Q(transaction__date__lt=period.start)
@@ -790,7 +778,7 @@ def balance_sheet(request, period_spec):
         brought_forward = Account.objects.get(code="3351")
         brought_forward.balance = -balance
         brought_forward.url = reverse(
-            "accounting:income-statement", args=[period.spec])
+            "accounting:income-statement", args=(period,))
         accounts.append(brought_forward)
     balance = Record.objects\
         .filter(
@@ -808,7 +796,7 @@ def balance_sheet(request, period_spec):
         net_income = Account.objects.get(code="3353")
         net_income.balance = -balance
         net_income.url = reverse(
-            "accounting:income-statement", args=[period.spec])
+            "accounting:income-statement", args=(period,))
         accounts.append(net_income)
     groups = list(Account.objects.filter(
         code__in=[x.code[:2] for x in accounts]))
@@ -861,22 +849,6 @@ def search(request):
     })
 
 
-def _get_period(period_spec):
-    """Obtains the period helper.
-
-    Args:
-        period_spec (str): The period specification.
-
-    Returns:
-        Period: The period helper.
-    """
-    first_txn = Transaction.objects.order_by("date").first()
-    data_start = first_txn.date if first_txn is not None else None
-    last_txn = Transaction.objects.order_by("-date").first()
-    data_end = last_txn.date if last_txn is not None else None
-    return Period(period_spec, data_start, data_end)
-
-
 def _cash_accounts():
     """Returns the cash accounts.
 
diff --git a/mia_core/period.py b/mia_core/period.py
index 2c25115..8960cfd 100644
--- a/mia_core/period.py
+++ b/mia_core/period.py
@@ -102,6 +102,10 @@ class Period:
     def description(self):
         return self._period.description
 
+    @property
+    def error(self):
+        return self._period.error
+
     @staticmethod
     def _get_last_month_start():
         """Returns the first day of the last month.
diff --git a/mia_core/templatetags/mia_core.py b/mia_core/templatetags/mia_core.py
index a9b3e25..41526e1 100644
--- a/mia_core/templatetags/mia_core.py
+++ b/mia_core/templatetags/mia_core.py
@@ -86,7 +86,7 @@ def url_period(context, period_spec):
         request.resolver_match.app_name,
         request.resolver_match.url_name)
     kwargs = request.resolver_match.kwargs
-    kwargs["period_spec"] = period_spec
+    kwargs["period"] = period_spec
     return reverse(view_name, kwargs=kwargs)