diff --git a/schema/deploy/trigger_functions/protect_date_overlap.sql b/schema/deploy/trigger_functions/protect_date_overlap.sql
new file mode 100644
index 0000000000..a0e6d4349a
--- /dev/null
+++ b/schema/deploy/trigger_functions/protect_date_overlap.sql
@@ -0,0 +1,31 @@
+-- Deploy ggircs-portal:trigger_functions/protect_date_overlap to pg
+-- requires: schema_ggircs_portal_private
+
+begin;
+  create or replace function ggircs_portal_private.protect_date_overlap()
+    returns trigger as $$
+  declare
+    temp_row record;
+
+  begin
+
+    for temp_row in
+      select * from ggircs_portal.reporting_year
+    loop
+      if (new.reporting_year != temp_row.year) then
+        if ((new.reporting_period_start between temp_row.reporting_period_start and temp_row.reporting_period_end)
+        or (new.reporting_period_end between temp_row.reporting_period_start and temp_row.reporting_period_end)
+        or (new.application_open_time between temp_row.application_open_time and temp_row.application_close_time)
+        or (new.application_close_time between temp_row.application_open_time and temp_row.application_close_time)) then
+          raise exception 'New date range entry overlaps with date range for reporting year %', temp_row.reporting_year;
+        end if;
+      end if;
+    end loop;
+
+    return new;
+  end;
+  $$ language plpgsql volatile;
+
+comment on function ggircs_portal_private.protect_date_overlap is 'Trigger function excepts if a date range in reporting_year overlaps with another row';
+
+commit;
diff --git a/schema/revert/trigger_functions/protect_date_overlap.sql b/schema/revert/trigger_functions/protect_date_overlap.sql
new file mode 100644
index 0000000000..3ba1793441
--- /dev/null
+++ b/schema/revert/trigger_functions/protect_date_overlap.sql
@@ -0,0 +1,7 @@
+-- Revert ggircs-portal:trigger_functions/protect_date_overlap from pg
+
+begin;
+
+drop function ggircs_portal_private.protect_date_overlap;
+
+commit;
diff --git a/schema/sqitch.plan b/schema/sqitch.plan
index 972ff343b6..090d5a61e4 100644
--- a/schema/sqitch.plan
+++ b/schema/sqitch.plan
@@ -197,4 +197,5 @@ computed_columns/application_revision_ciip_incentive [computed_columns/applicati
 @v1.10.1 2020-10-15T17:41:54Z Matthieu Foucault <matthieu@button.is> # release v1.10.1
 @v1.11.0 2020-10-22T00:27:09Z Dylan Leard <dylan@button.is> # release v1.11.0
 function_current_timestamp [function_current_timestamp@v1.10.1] 2020-10-30T23:15:30Z Pierre Bastianelli <pierre.bastianelli@gov.bc.ca> # Change ggircs_portal.current_timestamp() to use the mockable now() call instead
-@v1.12.0 2020-11-16T16:53:25Z Dylan Leard,,, <dleard@dleard-Aspire-V5-591G> # release v1.12.0
+@v1.12.0 2020-11-16T16:53:25Z Dylan Leard <dylan@button.is> # release v1.12.0
+trigger_functions/protect_date_overlap [schema_ggircs_portal_private] 2020-11-25T19:17:30Z Dylan Leard <dylan@button.is> # Trigger function to deny changes if a date range overlaps another
diff --git a/schema/verify/trigger_functions/protect_date_overlap.sql b/schema/verify/trigger_functions/protect_date_overlap.sql
new file mode 100644
index 0000000000..60046789d6
--- /dev/null
+++ b/schema/verify/trigger_functions/protect_date_overlap.sql
@@ -0,0 +1,7 @@
+-- Verify ggircs-portal:trigger_functions/protect_date_overlap on pg
+
+begin;
+
+select pg_get_functiondef('ggircs_portal_private.protect_date_overlap()'::regprocedure);
+
+rollback;