My ball might be lost or out of bounds. What should I do?

Play a provisional ball to save time. If your ball might be lost (outside a penalty area) or out of bounds, you may play another ball from where you just played.

• Announce it before you hit: you must use the word "provisional" or otherwise make it clear. Saying "I'll hit another" isn't enough; that ball becomes your ball in play under stroke and distance.
• You can keep playing the provisional until you reach the spot where the original is estimated to be.

Searching: a ball is lost if it isn't found within three minutes of you (or your caddie) starting to search.

What happens next:

• Original found on the course (outside a penalty area) within 3 minutes: abandon the provisional and play the original, no penalty.
• Original lost or out of bounds: the provisional is your ball in play, with one penalty stroke (stroke and distance). For example, a provisional from the tee is your third shot.
• If you play the provisional from nearer the hole than where the original is estimated to be, the provisional automatically becomes your ball in play.

No provisional played? If the ball is lost or out of bounds, you must go back and play from where you last played, adding one penalty stroke.

Your club may adopt a Local Rule allowing an alternative to going back; it applies only if the Committee has adopted it.

Source: Rules of Golf (2023), Rules 18.2, 18.3 and Definition of Lost.