When you send a payment to HMRC for your tax and national insurance on payroll, you should include a reference number which tells HMRC who the payment is from and to which month and year the payment relates to.

The reference number consists of your account reference number which you will have received when registering for PAYE plus four digits on the end which state the year and month  being paid. The year is the calendar year in which the current tax year ends, so for April 2012 to March 2013, the year code will be 13. The month code is the months number from the start of the tax year i.e. April is 01, May is 02 etc up to March as 12.

Example: December 2012 reference: [Ref: 123AB45678910][Year: 13][Month: 09]

So the reference you would use is: 123AB456789101309

Below is a list of the year and month codes for the current and next tax year:

April 2012: 1301
May 2012: 1302
June 2012: 1303
July 2012: 1304
August 2012: 1305
September 2012: 1306
October 2012: 1307
November 2012: 1308
December 2012: 1309
January 2013: 1310
February 2013:  1311
March 2013:  1312

Next Tax Year

April 2013: 1401
May 2013: 1402
June 2013: 1403
July 2013: 1404
August 2013: 1405
September 2013: 1406
October 2013: 1407
November 2013: 1408
December 2013: 1409
January 2014: 1410
February 2014: 1411
March 2014: 1412