What Is One Month Notice Period

1 ) 11 Month Agreement from 19 Jan 2019 to 18 Dec 2019 2 ) I Got one month notice from Tenants on 26 Sept 2019 that he is leaving early within one month , 3 ) So what should I have to do, I have taken rent from 19 Sept 2019 to 18 Sept 2019 But one notice period is going to complete on 26 Oct 2019, So Should I have to take full month rent of Month Oct 2019 or I have to take charges of those extra days ( from 18 Sept 2019 to 26 Oct ) ( It is 8 Days ) 4 ) Kindly advice