If I change my primary residence to a rental for any period and then sell it at a loss can I deduct the loss?

You will never be able to take a loss for the decrease in value during the time it was a personal use property. At best, you'll be able to take a loss for any further decrease in value after you convert it to a rental property. It is very important that you get an appraisal at the time you convert it.

If you sell it for a loss, your basis for determining a loss will be the lesser of the following two numbers:

1) The FMV of the property on day it was converted to rental use minus depreciation allowed or allowable.

2) The original adjusted basis of the property minus depreciation allowed or allowable.

On the other hand, your basis for determining a gain will be the original adjusted basis minus depreciation allowed or allowable.

If you have a gain use the loss basis and a loss using the gain basis, then your gain is considered to be zero.