In retirement, your outgoings are likely to be lower. For example, most retirees will have paid off their mortgage and their children will be financially independent. A general rule of thumb is that someone under the age of 40 would need 50% of their current net salary to have a good standard of living in retirement.
An easier target to focus on might be, 2/3rds of your net final a salary.
You should also think about the state pension. Under current rules this could be worth £ 9110 per year depending on your NI record.
You can check your State Pension and when you might receive it here https://www.gov.uk/check-state-pension
