My current extension of stay (retirement) was dated 25th June 2018 and has a permitted to stay date of 30th June 2019. According to my calculations this is 370 days. Is this an error? I thought extensions were for one year. (I should add that the last "admitted to" stamp in my passport is 30th June 2018, even though the extension is dated 25th June 2018).

Edited June 12, 20197 yr by johnny1966

The date that you do your extension doesn't change your period of stay.  It remains the same.

The 1-year extension period is determined from the expiry date of your current permission to stay (i.e. 30 June 2019 in your case), not from the date when you submit your application at your local immigration office (which could be up to 30 days earlier - or even 45 days earlier at 1 or 2 offices). 

Edited June 12, 20197 yr by OJAS

No error.