I still have 20+ days on my trial on total security 2018 but have purchased a key to take advantage of the sale in the UK. Does the years subscription start straight away, or when I activate my license?
Wait till your trial ends then activate your new license, that way you'll get and extra 20 days of coverage, if you activate it now it will start counting down and you will loose the last 20+ days of your trial.
Your license starts counting down the day you activate it.
DAMAN's reply sounds right. Chances are you will lose your remaining days when you have the Trial Version. However, for future reference, if you have the Paid Version, and BD sends out a lucrative (to you) promotion, your time remaining will automatically be ADDED to your new subscription.
120 days remaining + 365 days = 485 days on the new subscription.