I had a visa for 2012. Purchased an apartment overseas in 2007 befor I cam to the US. I came to the US in 2009. I rented out the apartment overseas as rental property. I recently sold it. does my cost basis start in 2009 or 2009 when I came to the US?

I guess you are a US resident either under the INS rule( i.e, permanent resident, a green card holder) or the IRS rule ( as a US resident for tax purposes), then your cost basis starts from the year of 2009 when you came the a US resident , NOT 2007 before becoming a US resident.

I was given a different answer as well. They used the Purchase Date. Is there somewhere that the rule is actually written?

As mentioned previously, your cost basis starts from the year of 2009 when you became a US resident , NOT 2007 before becoming a US resident. guess; 2009 cost basis can be larger than(or equal to) 2007 caost basisYou may contact an intl tax repre at the IRS for more info in detail.