Learn Icelandic: Jólaleyfið hefst eftir þrjár vikur. - The Christmas break begins in three weeks.

When talking about an event that will happen at a specific point in the future, Icelandic uses eftir followed by the amount of time in the accusative case. This structure translates to "in [amount of time]" in English. So eftir þrjár vikur means "in three weeks."

Why is the number three written as þrjár instead of þrír?

In Icelandic, the numbers 1 to 4 change their form to match the gender and case of the noun they describe. The word for "week" (vika) is feminine, and because it follows the preposition eftir, it must be in the accusative plural (vikur). Therefore, you must use the feminine accusative form of the number three, which is þrjár.

The verb hefst ends in -st. What does this mean?

It is the middle voice form of the verb hefja (to begin or elevate). When you add the -st ending, it becomes hefjast, which means "to begin" or "to start" (the break starts itself). You will often see this form used for schedules and events. The active verb byrjar would also work perfectly well here.

Why is the verb in the present tense (hefst) if the break is happening in the future?

Just like in English, Icelandic frequently uses the present tense to talk about scheduled future events. The time phrase eftir þrjár vikur makes it completely clear that the action is happening in the future, so no special future tense verbs are needed.