diff --git a/deploy/company.sql b/deploy/company.sql
index d07096f..ee5ea2f 100644
--- a/deploy/company.sql
+++ b/deploy/company.sql
@@ -26,6 +26,7 @@ create table company (
 	postal_code text not null,
 	country_code country_code not null references country,
 	currency_code currency_code not null references currency,
+	invoice_number_format text not null default '"FRA"YYYY0000',
 	created_at timestamptz not null default current_timestamp
 );
 
diff --git a/deploy/invoice_number_counter.sql b/deploy/invoice_number_counter.sql
new file mode 100644
index 0000000..255b8f3
--- /dev/null
+++ b/deploy/invoice_number_counter.sql
@@ -0,0 +1,32 @@
+-- Deploy numerus:invoice_number_counter to pg
+-- requires: schema_numerus
+-- requires: company
+
+begin;
+
+set search_path to numerus, public;
+
+create table invoice_number_counter (
+	company_id integer not null,
+	year integer not null constraint year_always_positive check(year > 0),
+	currval integer not null constraint counter_always_positive check(currval > 0),
+	primary key (company_id, year)
+);
+
+grant select, insert, update on table invoice_number_counter to invoicer;
+grant select, insert, update on table invoice_number_counter to admin;
+
+alter table invoice_number_counter enable row level security;
+
+create policy company_policy
+on invoice_number_counter
+using (
+	exists(
+		select 1
+		from company_user
+		join user_profile using (user_id)
+		where company_user.company_id = invoice_number_counter.company_id
+	)
+);
+
+commit;
diff --git a/deploy/next_invoice_number.sql b/deploy/next_invoice_number.sql
new file mode 100644
index 0000000..88cd46e
--- /dev/null
+++ b/deploy/next_invoice_number.sql
@@ -0,0 +1,38 @@
+-- Deploy numerus:next_invoice_number to pg
+-- requires: schema_numerus
+-- requires: invoice_number_counter
+
+begin;
+
+set search_path to numerus, public;
+
+create or replace function next_invoice_number(company integer, invoice_date date) returns text
+as
+$$
+declare
+	num integer;
+	invoice_number text;
+begin
+	insert into invoice_number_counter (company_id, year, currval)
+	values (next_invoice_number.company, date_part('year', invoice_date), 1)
+	on conflict (company_id, year) do
+	update
+	set currval = invoice_number_counter.currval + 1
+	returning currval
+	into num;
+
+	select to_char(invoice_date, to_char(num, 'FM' || replace(invoice_number_format, '"', '\""')))
+	into invoice_number
+	from company
+	where company_id = next_invoice_number.company;
+
+	return invoice_number;
+end;
+$$
+language plpgsql;
+
+revoke execute on function next_invoice_number(integer, date) from public;
+grant execute on function next_invoice_number(integer, date) to invoicer;
+grant execute on function next_invoice_number(integer, date) to admin;
+
+commit;
diff --git a/revert/invoice_number_counter.sql b/revert/invoice_number_counter.sql
new file mode 100644
index 0000000..8c18391
--- /dev/null
+++ b/revert/invoice_number_counter.sql
@@ -0,0 +1,7 @@
+-- Revert numerus:invoice_number_counter from pg
+
+begin;
+
+drop table if exists numerus.invoice_number_counter;
+
+commit;
diff --git a/revert/next_invoice_number.sql b/revert/next_invoice_number.sql
new file mode 100644
index 0000000..d7811bc
--- /dev/null
+++ b/revert/next_invoice_number.sql
@@ -0,0 +1,7 @@
+-- Revert numerus:next_invoice_number from pg
+
+begin;
+
+drop function if exists numerus.next_invoice_number(integer, date);
+
+commit;
diff --git a/sqitch.plan b/sqitch.plan
index 269ca73..001bbd5 100644
--- a/sqitch.plan
+++ b/sqitch.plan
@@ -54,3 +54,5 @@ edit_product [schema_numerus product product_tax parse_price company currency] 2
 invoice_product_tax [schema_numerus invoice_product tax tax_rate] 2023-02-15T13:20:30Z jordi fita mas <jordi@tandem.blog> # Add relation for taxes in invoice products
 new_invoice_product [schema_numerus] 2023-02-16T21:06:01Z jordi fita mas <jordi@tandem.blog> # Add type for passing products to new invoices
 add_invoice [schema_numerus invoice company currency parse_price new_invoice_product tax invoice_product invoice_product_tax] 2023-02-16T21:12:46Z jordi fita mas <jordi@tandem.blog> # Add function to create new invoices
+invoice_number_counter [schema_numerus company] 2023-02-17T13:04:48Z jordi fita mas <jordi@tandem.blog> # Add relation to count invoice numbers
+next_invoice_number [schema_numerus invoice_number_counter] 2023-02-17T13:21:48Z jordi fita mas <jordi@tandem.blog> # Add function to retrieve the next invoice number
diff --git a/test/company.sql b/test/company.sql
index fa0cff5..f53bbe4 100644
--- a/test/company.sql
+++ b/test/company.sql
@@ -5,7 +5,7 @@ reset client_min_messages;
 
 begin;
 
-select plan(80);
+select plan(85);
 
 set search_path to numerus, auth, public;
 
@@ -94,6 +94,12 @@ select col_type_is('company', 'currency_code', 'currency_code');
 select col_not_null('company', 'currency_code');
 select col_hasnt_default('company', 'currency_code');
 
+select has_column('company', 'invoice_number_format');
+select col_type_is('company', 'invoice_number_format', 'text');
+select col_not_null('company', 'invoice_number_format');
+select col_has_default('company', 'invoice_number_format');
+select col_default_is('company', 'invoice_number_format', '"FRA"YYYY0000');
+
 select has_column('company', 'created_at');
 select col_type_is('company', 'created_at', 'timestamp with time zone');
 select col_not_null('company', 'created_at');
diff --git a/test/invoice_number_counter.sql b/test/invoice_number_counter.sql
new file mode 100644
index 0000000..4601984
--- /dev/null
+++ b/test/invoice_number_counter.sql
@@ -0,0 +1,131 @@
+-- Test invoice_number_counter
+set client_min_messages to warning;
+create extension if not exists pgtap;
+reset client_min_messages;
+
+begin;
+
+select plan(25);
+
+set search_path to numerus, auth, public;
+
+select has_table('invoice_number_counter');
+select has_pk('invoice_number_counter' );
+select col_is_pk('invoice_number_counter', array['company_id', 'year']);
+
+select table_privs_are('invoice_number_counter', 'guest', array []::text[]);
+select table_privs_are('invoice_number_counter', 'invoicer', array ['SELECT', 'INSERT', 'UPDATE']);
+select table_privs_are('invoice_number_counter', 'admin', array ['SELECT', 'INSERT', 'UPDATE']);
+select table_privs_are('invoice_number_counter', 'authenticator', array []::text[]);
+
+select has_column('invoice_number_counter', 'company_id');
+select col_type_is('invoice_number_counter', 'company_id', 'integer');
+select col_not_null('invoice_number_counter', 'company_id');
+select col_hasnt_default('invoice_number_counter', 'company_id');
+
+select has_column('invoice_number_counter', 'year');
+select col_type_is('invoice_number_counter', 'year', 'integer');
+select col_not_null('invoice_number_counter', 'year');
+select col_hasnt_default('invoice_number_counter', 'year');
+
+select has_column('invoice_number_counter', 'currval');
+select col_type_is('invoice_number_counter', 'currval', 'integer');
+select col_not_null('invoice_number_counter', 'currval');
+select col_hasnt_default('invoice_number_counter', 'currval');
+
+
+set client_min_messages to warning;
+truncate invoice_number_counter cascade;
+truncate company_user cascade;
+truncate company cascade;
+truncate auth."user" cascade;
+reset client_min_messages;
+
+insert into auth."user" (user_id, email, name, password, role, cookie, cookie_expires_at)
+values (1, 'demo@tandem.blog', 'Demo', 'test', 'invoicer', '44facbb30d8a419dfd4bfbc44a4b5539d4970148dfc84bed0e', current_timestamp + interval '1 month')
+     , (5, 'admin@tandem.blog', 'Demo', 'test', 'admin', '12af4c88b528c2ad4222e3740496ecbc58e76e26f087657524', current_timestamp + interval '1 month')
+;
+
+insert into company (company_id, business_name, vatin, trade_name, phone, email, web, address, city, province, postal_code, country_code, currency_code)
+values (2, 'Company 2', 'XX123', '', '555-555-555', 'a@a', '', '', '', '', '', 'ES', 'EUR')
+     , (4, 'Company 4', 'XX234', '', '666-666-666', 'b@b', '', '', '', '', '', 'FR', 'USD')
+;
+
+insert into company_user (company_id, user_id)
+values (2, 1)
+     , (4, 5)
+;
+
+insert into contact (contact_id, company_id, business_name, vatin, trade_name, phone, email, web, address, city, province, postal_code, country_code)
+values (6, 2, 'Contact 1', 'XX555', '', '777-777-777', 'c@c', '', '', '', '', '', 'ES')
+     , (8, 4, 'Contact 2', 'XX666', '', '888-888-888', 'd@d', '', '', '', '', '', 'ES')
+;
+
+insert into invoice_number_counter (company_id, year, currval)
+values (2, 2010, 6)
+     , (2, 2011, 8)
+     , (4, 2010, 8)
+     , (4, 2012, 10)
+;
+
+
+prepare counter_data as
+select company_id, year, currval
+from invoice_number_counter
+;
+
+set role invoicer;
+select is_empty('counter_data', 'Should show no data when cookie is not set yet');
+reset role;
+
+select set_cookie('44facbb30d8a419dfd4bfbc44a4b5539d4970148dfc84bed0e/demo@tandem.blog');
+select bag_eq(
+	'counter_data',
+	$$ values (2, 2010, 6)
+	        , (2, 2011, 8)
+	$$,
+	'Should only list invoices of the companies where demo@tandem.blog is user of'
+);
+reset role;
+
+select set_cookie('12af4c88b528c2ad4222e3740496ecbc58e76e26f087657524/admin@tandem.blog');
+select bag_eq(
+	'counter_data',
+	$$ values (4, 2010, 8)
+	        , (4, 2012, 10)
+	$$,
+	'Should only list invoices of the companies where admin@tandem.blog is user of'
+);
+reset role;
+
+select set_cookie('not-a-cookie');
+select throws_ok(
+	'counter_data',
+	'42501', 'permission denied for table invoice_number_counter',
+	'Should not allow select to guest users'
+);
+reset role;
+
+
+select throws_ok( $$
+	insert into invoice_number_counter (company_id, year, currval)
+	values (2, 2008, 0)
+	$$,
+       '23514', 'new row for relation "invoice_number_counter" violates check constraint "counter_always_positive"',
+	'Should not allow starting a counter from zero'
+);
+
+select throws_ok( $$
+	insert into invoice_number_counter (company_id, year, currval)
+	values (2, -2008, 1)
+	$$,
+       '23514', 'new row for relation "invoice_number_counter" violates check constraint "year_always_positive"',
+	'Should not allow counters for invoices issued before Jesus Christ was born'
+);
+
+
+select *
+from finish();
+
+rollback;
+
diff --git a/test/next_invoice_number.sql b/test/next_invoice_number.sql
new file mode 100644
index 0000000..c23443a
--- /dev/null
+++ b/test/next_invoice_number.sql
@@ -0,0 +1,50 @@
+-- Test next_invoice_number
+set client_min_messages to warning;
+create extension if not exists pgtap;
+reset client_min_messages;
+
+begin;
+
+select plan(17);
+
+set search_path to numerus, public;
+
+select has_function('numerus', 'next_invoice_number', array ['integer', 'date']);
+select function_lang_is('numerus', 'next_invoice_number', array ['integer', 'date'], 'plpgsql');
+select function_returns('numerus', 'next_invoice_number', array ['integer', 'date'], 'text');
+select isnt_definer('numerus', 'next_invoice_number', array ['integer', 'date']);
+select volatility_is('numerus', 'next_invoice_number', array ['integer', 'date'], 'volatile');
+select function_privs_are('numerus', 'next_invoice_number', array ['integer', 'date'], 'guest', array []::text[]);
+select function_privs_are('numerus', 'next_invoice_number', array ['integer', 'date'], 'invoicer', array ['EXECUTE']);
+select function_privs_are('numerus', 'next_invoice_number', array ['integer', 'date'], 'admin', array ['EXECUTE']);
+select function_privs_are('numerus', 'next_invoice_number', array ['integer', 'date'], 'authenticator', array []::text[]);
+
+
+set client_min_messages to warning;
+truncate invoice_number_counter cascade;
+truncate company cascade;
+reset client_min_messages;
+
+insert into company (company_id, business_name, vatin, trade_name, phone, email, web, address, city, province, postal_code, country_code, currency_code, invoice_number_format)
+values (1, 'Company 2', 'XX123', '', '555-555-555', 'a@a', '', '', '', '', '', 'ES', 'EUR', '"F"YYYY0000')
+     , (2, 'Company 4', 'XX234', '', '666-666-666', 'b@b', '', '', '', '', '', 'FR', 'USD', '"INV"000-YY')
+;
+
+insert into invoice_number_counter (company_id, year, currval)
+values (1, 2010, 5)
+     , (2, 2010, 6)
+;
+
+select is( next_invoice_number(1, '2010-12-25'), 'F20100006' );
+select is( next_invoice_number(2, '2010-12-25'), 'INV007-10' );
+select is( next_invoice_number(1, '2010-10-17'), 'F20100007' );
+select is( next_invoice_number(2, '2010-10-17'), 'INV008-10' );
+select is( next_invoice_number(1, '2011-12-25'), 'F20110001' );
+select is( next_invoice_number(2, '2012-12-25'), 'INV001-12' );
+select is( next_invoice_number(1, '2011-12-25'), 'F20110002' );
+select is( next_invoice_number(2, '2012-12-25'), 'INV002-12' );
+
+select *
+from finish();
+
+rollback;
diff --git a/verify/company.sql b/verify/company.sql
index c9793a5..bd21fd7 100644
--- a/verify/company.sql
+++ b/verify/company.sql
@@ -16,6 +16,7 @@ select company_id
      , postal_code
      , country_code
      , currency_code
+     , invoice_number_format
      , created_at
 from numerus.company
 where false;
diff --git a/verify/invoice_number_counter.sql b/verify/invoice_number_counter.sql
new file mode 100644
index 0000000..db453f7
--- /dev/null
+++ b/verify/invoice_number_counter.sql
@@ -0,0 +1,14 @@
+-- Verify numerus:invoice_number_counter on pg
+
+begin;
+
+select company_id
+     , year
+     , currval
+from numerus.invoice_number_counter
+where false;
+
+select 1 / count(*) from pg_class where oid = 'numerus.invoice_number_counter'::regclass and relrowsecurity;
+select 1 / count(*) from pg_policy where polname = 'company_policy' and polrelid = 'numerus.invoice_number_counter'::regclass;
+
+rollback;
diff --git a/verify/next_invoice_number.sql b/verify/next_invoice_number.sql
new file mode 100644
index 0000000..966bd0a
--- /dev/null
+++ b/verify/next_invoice_number.sql
@@ -0,0 +1,7 @@
+-- Verify numerus:next_invoice_number on pg
+
+begin;
+
+select has_function_privilege('numerus.next_invoice_number(integer, date)', 'execute');
+
+rollback;