For single trip policies, select the day you depart for your destination. From the date you buy your policy, you'll have cancellation cover regardless of whether the policy has started. Therefore, it's important to buy your travel insurance as early in advance as possible, as soon as you have your trip booked.
Annual policies cover you for 12 months from the start date. It’s best to buy the policy in advance of your first trip to give you cancellation cover straight away.