Without any sarcasm intended: When your lease says it starts.
You and the LL were contractually bound to one another when you both signed. That does not confer physical possession.
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Usually what the lease says is the start date absent some other document to the contrary or some earlier date where possession is taken.
Neither the date of the signing of the lease nor the day rent payment is first due governs. As my colleague stated, the lease itself provides the dates.
Example: I could sign a lease today which requires me to pay rent on January 15, 2014 for a lease term that starts February 1, 2014.
Now, if the lease is silent on the start and end dates.....another story. But first look to the writing.
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