I used the ROS online system last year (2009) for the first time to complete my income tax return. I have rental and paye income. I found it very easy to use. I had no tax liability for 2008. So I paid no additional tax that year. This year I completed my tax return online and I had a tax liability of about 9,000 for 2009. My question is should I have paid some of this liability in 2009 as a prelimerary amount ?