Forms P11D, P9D and P11D(b) must reach HMRC by 6 July following the end of the tax year. 

Your payment of the Class 1A NICs declared on form P11D(b) must reach HMRC by 22 July, or by 19 July if you pay by cheque. 

The process of gathering the necessary information can take a long time, while the P11D appears a quite innocuous two-page form, there is a lot of detail and effort required to get the data on it correct so it is important that this process is not left to the last minute. 

With GTax P11D calculation and online submission this process can be substantially simplified, with real-time data validation and correction, you make sure you only submit accurate P11D and P46 Car details to HMRC.