The expiration date of peanut butter is just a general guideline as to when the peanut butter will stop being fresh and it's recommended to eat the peanut butte on the expiration date or before the expiration date for best taste and freshness.
But as long as the jar of peanut butter has remained sealed the peanut butter can last a year or even longer past it's expiration date.
The peanut butter is only bad if it smells bad or has mold growth in it but as long as it smells good, tastes good and has no mold the peanut butter is very safe to eat.
If you want the freshest taste from the peanut butter you should eat it before the expiration date but there's not need to throw the peanut butter out when it expires.
Peanut butter lasts a long time as long as it remains sealed and doesn't need refrigeration.