Inform Often and Completely
When you’re going to miss a deadline or be late for work, it’s always best to inform those who need to know before it happens. It’s difficult and awkward having to explain why you couldn’t get something done or why you were late to the meeting, but if you know there’s a chance you’ll miss the mark, inform people earlier rather than on the same day.
Texting or calling that you’re going to be late looks irresponsible. Telling your boss three days before it happens seems organized and thought-out. It will also develop trust in your character when nothing is delayed or cancelled last minute. Be ahead of the curve.