Vehicle Excise Duty is not one flat fee. In the first year most petrol and diesel cars are taxed from a CO2 table. From year two they move to a standard rate (around £195 for 2025/26). Zero-emission cars have a low first-year amount, then the same standard rate.
If the list price when new was more than £40,000, an extra annual amount is added for five years from the second licence. That is on top of the standard rate. Check the list price, not what you paid at the dealer.
Tax it officially
The amount you actually pay is on GOV.UK when you tax the vehicle. The UK car tax calculator uses published bands so you can budget. Save the expiry in CarDiary with the MOT date so both reminders land in the same place.