A possibly stupid giving notice question

[SarfEast1cated]

I haven't done it for over 16yrs so am a bit out of practice. I need to start my new project on the 9th September. I have to give one months notice. When should I hand in my letter? 8th August? or is 4 weeks and therefore 12th August? I can't work it out .
Thanks for you help (and not mocking my ignorance)...

I'd hand it in on the 8th August in case it is a calendar month rather than 4 weeks.

They have already filled my position with an internal person so they don't really need time to recruit...

Whether it's a month or 4 weeks will be in your contract so that's easy for you to check and not something we can advise you on.

But I'm confused- why wait? If they've replaced you they know you're going so why leave it? Just hand it in now, specifying an end date of 8 September. There's nothing stopping you giving more notice than you have to.

I have some treatment scheduled on my private health insurance, and as soon as I give my notice in the cover stops. Therefore I want to leave it as long as possible really.

Ok well in that case check your contract. If it says a month, 8 August, if it says 4 weeks then 12 August.