I stayed in an apartment in seattle wa with no lease for 4 months , and I want now to move out, I was told I have to give them a written notice and pay for an extra month rent , am I legally obliged to do that... I offered a prorated payment instead!

You are on a month to month basis. Therefore you have to give notice at least 20 days prior to the end of the rental period. If you don't, then you are responsible for the full rent for the next month.

http://www.wsba.org/media/publications/pamphlets/landlord-tenant.htm

I stayed in an apartment in seattle wa with no lease for 4 months , and I want now to move out, I was told I have to give them a written notice and pay for an extra month rent , am I legally obliged to do that.... I offered a prorated payment instead!!


You have to pay on the same basis you paid rent - if it was the 1st of every month then you have to give written notice BEFORE the 1st of the month, pay for that next month, be out the 1st after that.

No, you cannot legally prorate rent.