
This all depends on your agreement (aka. your lease). If you have a fixed term agreement (current lease) the rent cannot be increased unless a 'special term' in your agreement states. This special term will include the amount of the increase or how the increase is to be worked out. In this case your lessor/agent/owner must give you notice in writing before increasing the rent. Usually around one month - depending on the laws in your state.
Although, if you do not have a current lease you will most likely be on a periodic agreement. In this situation the rent can be increased at anytime. The lessor/agent/owner must give notice in writing before increasing the rent. Usually around 2 months - depending on the laws in your state.
If your lease expires and is not renewed your rent can be increased at anytime. Moral of the story - make sure your lease is current!
If you think your rent increase is excessive you should contact your State Authority for advice.
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