Stating your contract rate is equivalent to stating your previous salary. Converting between the two is relatively easy if you know the extra benefits that come with being an employee. You can check the many many other questions on this site about when to state your previous salary, but in general stating it puts you at a disadvantage. Knowing your previous salary (or equivalent in contract rate) means the company can pitch you a salary which they know is better than your current one, and that you are therefore unlikely to reject, but is lower than they might otherwise have offered. If they don't know your salary (or contract rate) then they might offer you something much higher.
If they pitch you something that works out being equivalent to less than your contract rate, then you can always tell them your contract rate at that point.
However if you are going to be happy with something that is the same as your contract rate (after allowing for employee benefits) then by all means tell it to them. The difference between your contract rate and your salary is that your salary is extremely hard to change once established, whereas your contract rate can be renegotiated for each contract.