The good news is that Magnesium Carbonate is a pretty inert product that essentially does not go bad. Most chalk powder will stay good way beyond the expiration date on the packaging. ... Chalk that has not been stored properly will over time take up some from the air & will start to feel less effective.

How long does chalk last?

But to give you a rough idea, we've found that a chalk piece drawn onto standard sidewalk cement will last 5-10 days in great condition if left untouched in gorgeous California weather. We've seen pieces last as long as one month or more at 75% quality.

Can chalk go stale?

Chalk is an almost completely inert chemical & stays good far beyond the expiration date on the label that is essentially only there to comply with regulations. It does not expire the same way food does.