Deadline for submission of 2015/16 self assessment returns if you require HMRC to compute your tax liability and/or if tax underpaid is to be collected by adjustment to your 2017/18 PAYE code
This deadline is only relevant for those individuals who complete a 'paper' self assessment tax return and who are employees. Where you have an underpayment you may request that HMRC collect the tax outstanding by making an adjustment to your tax code for the year 2017/18.
Please note that where your return is submitted online then the filing deadline for 'coding out' is 30 December 2016.
If we are already dealing with this matter on your behalf you need take no action.