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UKBA allows applications for the 10 year long residence ILR to be submitted up to 28 days in advance of the qualifying continuous residence period.

In my case, I first entered the UK on 22/08/2009, my current visa will be expired on 31/07/2019, I was wondering I can only submit it from 26/07/2019 (counted 28 days according to 22/08/2019) or from 25/07/2019 (counted 28 days according to 9 years 11 months 2 days)?

Thanks.

You can apply no sooner than anytime within 28 days before the 10th anniversary of the date you entered the UK. It is not mandatory to apply on exactly the 28th day.

https://www.timeanddate.com/date/datead ... ad=28&rec=

Sorry, my question is that, if I counted 28 days according to 22/08/2019, which means that I can apply from 26/07/2019. However, if I counted 28 days according to 9 years 11 months 2 days, which means I can apply from 24/07/2019.

You count from the date you ENTERED the UK, not 9 years 11 months 2 days as some months have 31 days.