PMI, short for Primary Mortgage Insurance, is extra insurance that lenders require from most homebuyers who obtain loans that are more than 80% of their new homes value.  It is important to factor this cost into your principal, interest, taxes and insurance to get an accurate depiction of your true monthly investment for your home loan. 

Here is an estimate of what PMI would run for different scenarios based on a 30 amoritorized loan:

Take loan amount x PMI factor / 12 for your monthly premium.  (LTV = Loan to Value)

LTV 80% or below = 0

80.01 – 85% = .38

85.01 – 90% = .62

90.01 – 95% = .94

95.01 – 97% = 1.10