Why can't you print an Islamic calendar out in advance?

Because the Islamic calendar is based on the moon cycle, it is possible to print or write out a rough estimate of when a new month will begin, but this estimate will not necessarily be precise. That's because the month begins at the exact moment when a human observer can see the first lunar crescent after a new moon.

This means that factors such as cloudy weather and a person's exact location on Earth will have an impact on when the month is said to start. People who follow this calendar can either defer to official sources or use their own observation to determine the start of a new month.