Period of tax calculation

On page 22 of F6 Notes, Example 4 of 'Lease premiums on grant of short lease': 'Qustion: Bill grants Richard a lease to a shop on 30 June 2014, Annual rent £5,000 due on 1 July 2014, Term: 20 years, Premium: £60,000, Calculate the Property Income assessment for Bill in 2014/15. Answer: Premium (51-20)/50*60,000 =37,200, Rent 9/12*5,000 =3,750, Property Income =37,200+3,750 =40,950'. My question is on 'Rent 9/12*5,000 =3,750', rent start from July, so why the period is 9 months, not 6 (July~Dec)? Thanks!