30 Day Growth is the change in value of your Total Net Worth during the last month. 

Please note that if you don't update your valuations and balances regularly, this metric may appear larger than it really is. For example, if you bought a house for USD 100,000 five years ago, and only updated its value once five days ago (to USD 110,000 for example), the 30 Day Growth metric will say that your investments have grown by 10,000 in the last month.