Par rate is the base rate charged by a lender, this rate requires no buy down and the broker gets no Yield Spread Premium (YSP). This rate is pre-adjustments, fees, or yield spread premiums charged by the broker. The Par Rate is then adjusted based on several factors such as your credit score, the loan to value ratio, whether it is an FHA or Conventional loan, and how long you want to lock the rate for.:
Your Fico is going to play a part in determining your base rate, the better your score the better your rate is going to be, a 720 or higher is going to provide the best rate without penalty. Lower than 720 and you are looking at potentially .50 to .75 point penalties depending on the lender.
Loan to Value:
Your percentage of equity vs your mortgage is taken into consideration in determining your base rate. While everyone tells you to shoot for no more than 80%, the rate schedule I am referencing actually penalizes you more for being between 75%-80% LTV
FHA Vs. Conventional:
Whether or not you choose to go conventional vs. FHA is going to affect the base rate, FHA loans are more limited in the funding options than conventional mortgages.
The length of time you choose to lock your rate for could also affect your final rate. Where par may be 4.625% for a 21 day lock, it could be 4.750 for a 35 day lock. You have a better chance of getting a lower rate the less time you need to get your loan funded.