If you get Council Tax support
Council Tax Reduction
Changes which affect the amount of Council Tax Reduction you are entitled to must be reported within 21 days. This may include changes to your benefits, income, capital and household composition.
Single Occupancy Discount
If you are in receipt of Single Occupancy Discount, then you should report if someone comes to stay with you for a period of time or someone in your household turns 18 years of age.