as was mentioned above,use coinwarz calc,it is better,also substract approximately 10-15% total due to
unforseen troubles like:blackouts,system failures,you beeing unable to fire the miners up,random disconnets etc.
with only one GPU you will not be able to mine anything decent,maybe some LTC or ZEC but it will be not more than 50-60$ per month
and generally not worth it
although you can try it for a month and if you are happy with the results,purchase or assemble a separate rig with 5-6 gpus
these are only second profitable to altcoin asics at the moment and ROI in under 5 months on average