Defaulting values for a calculation tool

I've been asked to build a repayment calculator for a bank and 85% of their customers are of a specific type, e.g. Married, over the age of 30 first time buyer etc, you get the idea.

Now, depending what customer type you are the calculation applies different interest rates. We're thinking "well if 85% are a specific type, why can't we default the state of the calculator to this user group?" The calculator will say 'Married' 'over 30' etc and allow the user to change if they are not of this group.

How might users react to this? It would mean 85% of users have to enter less data but the 15% ....well, is there a danger in this approach?

I'm looking for specific citations

edit: forgot to add, if a user does not notice the default states and goes ahead they will get the wrong loan amount told to them and this is potentially disastrous to the business