Child turning 18

My son has just turned 18 and is about to complete his college course. No plans yet but unlikely to enrol in September for another year.
When do I advise child benefits and the tax credits office, now or in September?

If I was you I would ring them and explain what the position is that your son finished his college course and isn''t sure if he will continue at college for another course. They will tell you what the position is. From what I understand CTC ceases on the last day the child is in school/college - ie usually the day they had their last exam.
If you keep them informed and they continue to pay you that way they can''t ask for the overpayments back come September if he doesn''t continue with his education. I know someone who didn''t tell them and had to pay the money back. Best keep them in the picture - only my view though I''m sure others will have their own opinions on it.

Something made me think that there was a grace period up to September. I would rather not phone them unless I have to. I can''t afford to spend an hour waiting on the line.

I think you will find it will automatically end on the 31 August.

I think you only have to advise them earlier if your child starts work.

CB ends on the first Monday in September

Look on www.gov.uk - CTC cease the last day your child is in school/college - CB is different usually ends 31st August.
I rang them recently and was only holding for 5 minutes but maybe yours is a different area which is busier.
They do always say to notify them of changes and if your child has finished school they may consider that a change in circumstance?

When I phone CTC one of two things happens.
I go through endless options. I tell the recorded message 4 or 5 times I want to talk about tax credits, 4 or 5 my name is on the claim, 7 or 8 times my NI number, listen to endless recordings then get told they are to busy to talk to me goodbye or I hold on for 45 minutes then manage to talk to somebody.
CTC don''t actually pay me anything anyway so I don''t see the big hurry to tell them if it means hanging on the phone all day. May just write to them.