I've been using a payroll package to calculate and export my p30 returns for my sole employee throughout the year. For some reason after I switched from paying my employee weekly to monthly, the software understated the payment amount to ROS by about 300/ per quarter. Now. as I understand it, the p35 form is meant to take care of that. I just made a correct p30 payment for the last quarter of 2012 but when I get my software to generate the p35 file and export it to ros, the amount I owe is much more than I believe it should be. If I leave uploading the p35 form to ros until after the p30 payment is deducted from my account, will the amount I owe go down. I don't have the head to submit the payment manually and am totally dependent on the software I use.