How long does a monthly subscription last?

If I upgrade to silver tomorrow, will it last through the calendar month of March, or for 30 days? Just trying to figure out a deadline.

A monthly subscription will be active during 30 days starting the day you purchased it, for example, if you purchase your subscription your subscription on March 1st, the next renewal will be on April 1st, please note that JotForm subscriptions are automatically renewed so if you want to stop the renewal you will need to downgrade back to free. 

https://www.jotform.com/help/341-How-to-Cancel-a-Subscription-and-downgrade-back-to-free 

I hope this helps.