The council must decide a major application within 13 weeks, and other applications within 8 weeks, unless you agree a longer period in writing. Applications that need an Environmental Impact Assessment have 16 weeks.
Reply promptly when the case officer asks for more information, and follow the comments from neighbours and consultees on the council's website so you can deal with points before they become reasons for refusal. If the council asks for more time, you can agree an extension of time in writing. If you do not, you can appeal against non-determination once the period ends.
If a major application is still undecided after 26 weeks, or another application after 16 weeks, and you have not appealed or agreed a longer period, the council refunds your application fee.
Many decisions are taken by planning officers. Some go to the council's planning committee. If yours does, read the officer's report when it is published, and check the council's rules on whether and for how long you can speak at the meeting.