Hi Kimberly,

Thank you for contacting the UNH Extension Infoline with your question about when the last spring frost date is.  In a blog from 2021, Master Gardener Will Lowenthal notes that “Memorial Day, always the last Monday in May, is a traditional guide to the last frost date of the season in central New Hampshire. You can adjust this by a week or so depending on where you live, but remember the weather does not always respect the calendar!"

https://www.nrcc.cornell.edu/services/blog/2011/05/10_last_frost/index.html  This link provides a map showing a range of dates depending on where one lives in NH.  The information is based on the average frost dates over several years. 

Other resources note that for zone 5 the last frost date is late May.